I only have rollers but I do like them quite a bit...As Dalai said, they're not very good for intervals unless you get a resistance unit. For a max effort the only thing stopping me is cadence...letting some air out of the tires adds resistance but noise goes up with it and I can still hit 130rpm in 53/12 (and I'm sure 53/11 if I switch cassettes).
I've only ridden my TT bike on them once but I had never gone down on the aero bars. It's something I'm going to be looking into doing in a month or so when I get my front derailleur fixed.
I don't see there being any issue with it. It could help you a lot for triathlon as rollers cause you to develop a more efficient and smoother pedal stroke to stay balanced. If you mash and throw your weight around on rollers your bike moves around too.
I don't own a trainer but if I can't find a good resistance unit for my rollers I'll be getting one for later in the winter when I start to train for speed/strength.
Bottom line...even if I get a trainer for hard workouts it's not going to replace my rollers. I'd just be doing what Dalai does