There are various factors involved in how I think about these skills.
You can coach a DL in DBZ, whereas you can't coach the other skills to this types of players. That makes the skill slightly less valuable, IMO. In old GP I like DBZ, as it's a strong tool. I don't find it anywhere near as valuable in Nu GP. I like to have my DL line stacked in Old GP, and DBZ on the DL is therefore more valuable in old GP when comparing the two versions. I like to have the trenches stacked generally, anyway.
The OQB on a RB is very useful, especially if it's a 3* RB, as people don't think he's got OQB and can think you are weak in that area if your O line is not stacked. They keep blitzing, but not seeing the success that they would expect. That said, I don't think an OQB RB offers much more from a pure OQB perspective than just having a stacked O line when looking at the individual skill, although you might see occasional blitz pick ups. That said I do not know how many more blitz pickups you would see with the OQB RB than without (something for more skilled statisticians than me to look at potentially). All in all, I do like to have an OQB RB to see these occasional blitz pickups, but it is icing on the cake really.
I really like DPS on LBs. I have no stats to back me up, but I feel that there are far more picks with a DPS LB in place. I used to operate a 3-4 in NFLA with 2 veteran 4* LBs and the D was just amazing. Turnover central.
I have changed my mind a couple of times, but will say:-
1) DL DBZ (I want the line stacked)
2) LB DPS (Turnovers)
3) RB OQB (Useful, but not as much as the ones above)
Edit - Just spotted that I read the question wrong. It was DB DBZ, not DL DBZ! D'oh!
DB DBZ and LB DPS useful, but especially if you call plays that emphasise them. If you blitz a DB you'll have more success if you have a DB with DBZ. Similarly a play like LD should benefit from a LB with DPS.
Alas, one of the gripes of large roster sizes is that pretty much every team ends up having players with these skills so the whole usefulness things becomes diluted.
I have an impressive 28 blitz pick-ups this season, that equates to 20% of passes called against a blitz - compared to an opposition figure of 7%.
Last season these figures were 12% and 7%. This season I have both FB and TE with OQB (sadly both likely to retire) .
Leading on from Jacko's comment on roster sizes, I agree they are generally too high, thus negating somewhat 'taking advantage of an assumed weakness in the opposition'.
At start of the current season the average roster was nearly 62 in NFLC (I think the League Roundup totals ignore extra special team totals).
That's heading towards 3 per starter, especially late in the season with FA and coaching.
Limiting it to 48 (2 per starter and BQ, 1 per kicker) would mean teams would have areas of strength and weakness.
You can have 3, 4, 5 star players but that means more 1 and 0 star starters.
Extra special teams strengths would be hidden (WR with OPL and DKR shows as 1 star) and more of a wild card.
Training weak areas would be more important and trying to work out and exploit opponents a greater part of the weekly plan.
A pointless discussion on 'Old Gameplan' as this isn't going to change but is there anything like this in 'Nu' ?
Does the sheer scale of formation, skills, signature plays etc mean that there are always going to be 'exploits' there ?
Are you able to spot these with careful research or would you need to scout specifics (seem to remember scouting was there somewhere) ?
Probably should have put this in the Nu area rather than here.