Can be done either way, whether transfer right away or drip acclimate them again before adding..
If parameters match up fairly close, I think it's less stressful to add them right away, so you aren't catching and releasing them twice (net to drip container, container to tank).
But if parameters aren't exactly close, or going from non-co2 to injected co2, then I would drip acclimate to be on the safe side.
For a extra precaution, you can turn the lights off for a while to have the new fish feel safer in the dark until they learn that their new environment is safe.
I do, do what Bushkill does as well as far as the group being drip acclimated and single fish straight over. I do have medium size Marina hang on breeders, but I don't acclimate in them, I just use a bucket for now. Haven't really thought through which is more stressful, having the stressed fish in a dark bucket acclimating then transferring into a new tank that have never seen before, or acclimating in the clear breeder getting to see into the tank and becoming somewhat acquainted with the surroundings/inhabitants before being released, but then again they might feel more stressed being in a clear confined box which no where to really escape/hide from the other visible fish (unless the breeder is planted I guess). Just haven't dawned on it much which would be less stressful to make up my mind yet. I guess it depends on the fish species though (in tank and in container/bucket).