Yes it is, marginally, 105.3 on, 104.4 off, that's a 0.9 difference. This could mean that the defense is better without DJ, this could mean that Ryan Hollins despite his fouling does a lot of other things really well on defense to make up for it, this could mean that DJ plays with non-favorable defensive lineups more than other starters, so we'll have to get some context.
Most (all?) teams starters have a higher Ortg than their bench, so if the opposing bench and starters played equal level defense, their bench would have a lower Drtg because they are playing against an inferior offense. If the bench and starters have the same Drtg, then your starters are actually the better defensive unit because they are accomplishing the same defense against better offensive players. If your starters have a significantly better one (like 2 pts/100), then they are much better
If DJ is primarily on with the starters, then he's on mostly with the other teams best offensive players. Okay, so let's look at CP and Blake to see how this plays out.
CP: On (103.1) / Off (107.5) = (-4.4)
Blake: On (104.5) / Off (106.4) = (-1.9)
*Minus being a good thing, meaning the team is giving up less points, just so no one is wondering why that seems odd
Now, the starters don't play ALL their minutes together, but here we see that in contrast to DJ, the team has lower Drtg with Paul and Blake on than off, so that doesn't help DJ. Does this say DJ is a bad defender? No, not at all, but it does suggest that he is probably not a dominant defender (but then again, we already knew this didn't we?). It could also be a product of the minutes he isn't with the other starters, maybe in those minutes he's with poor defensive units.
Here are on/off numbers that would suggest dominant defensive impact on that team:
Marc Gasol 12-13: on (98.2) / off (105.1)
...but context is important, wasn't Marc Gasol always on with Conley and Allen?
Allen 12-13: on (97.2) / Off (103.8)
Conley 12-13: on (97.8) / Off (105.9)
So this seems to suggest more of a starting lineup that is dominant defensively as a unit, without a clear highest impact guy being suggested, but you would need to examine other things to get a better understanding such as who everyone is playing with, who is the main cog in keeping the defense intact. This season with Allen coming off the bench, we see this:
Allen: on (103.3) / off (105.4)
M.Gasol: on (105.1) / off (104.3)
M.Conley: on (106.2) / off (102.4)
Is this significant? Well, Allen is now coming off the bench (28/52) games in favor of the better shooter in Lee. He has the best on/off defensive numbers, so this seems to suggest that maybe Allen (who played 79 games last season) is actually their highest impact defender of the three...but he's also now playing against more benches / bench players, and maybe he's just getting put in more favorable lineups, so this alone can't be used to conclude anything. We'd need some good film analysis and some other supporting numbers at least.
In the end though, something like Defensive RAPM would give you a more accurate description, high and low players put for reference.
Andre Iguodala: 5.5
Kevin Garnett / Larry Sanders: 4.2
Marc Gasol: 4.1 (Allen - 2.4 , Conley - 1.8, Gasol still wins)
Tim Duncan: 3.4
Dwight Howard: 3.3
Amir Johnson: 2.6
Patrick Beverly: 2.5 (Harden: -1.2)
Chris Paul: 1.8
Blake Griffin: 1.5
DeAndre Jordan: 0.6
Marco Belinelli: -3.0
Jimmer Fredette: -3.2
Eric Gordon: -3.5
Gary Neal: -3.7
Byron Mullens: -4.5
We see a good correlation to who we consider good defenders and who we consider bad defenders, so that gives us some validity confidence. RAPM seems to line up with the basic on/off that DJ is an averageish overall impact defender and Blake and Paul have been the ones who are more "plus" defenders this season.
Other Clippers Defensive RAPM
Davis and Granger are not Clipper numbers, those are season numbers. Again, RAPM is not a be all / end all, it is better to look at it over multiple seasons and if patterns continue, then it is more suggestive of whatever it was saying. The Clippers most mis-matched position is starting SG. Collison and Redick have played the most minutes there, so maybe there is a correlation with them being the lowest.
Hollins comes out with flying colors here, he does have the hustle, I'll give him that. All the SF's have shown the be almost exactly the same range on defense and all quite average. Paul being a good and positive impact defender (which we all already know this season) is supported by him being the only positive guard on the team, and Will the closest is 2 points back (1.8 to -0.2).
Seriously Mullens? Only player with a -4 or lower defensive RAPM, I didn't think it was that bad. Iguodala has been great for Golden State despite the not so impressive raw numbers, he's brought great defensive impact, and there are a lot of things supporting his defensive impact for them. Him and Bogut's defense is going to be the biggest factor for Golden State doing anything in the post-season after / in conjunction with the shooting and the play of Curry.
RAPM Reference: http://stats-for-the-nba.appspot.com/ratings/2014.html
Basketball-Reference for On/Off stats