I find that if I learn a song from the singing of another singer (particularly from tapes/cds)I might pick up the quirk, however after a few performances and intimate contact with the song I'll begin to drop them (known to do that after a few pints too!).

However, sometimes I find these quirks are also interesting techniques which can be used in other songs (some of Christy Moore's vocal mannersims for example)which might be utilised (sans accent of course).

I'm sure more than a few of my techniques have been picked up from someone else and incorporated. I dare say it's pretty common. I don't think I'd deliberately set out to imitate another singer unless it was for a parody or something.