I've never seen bag babies before, at least not that I'm aware of, but I'll have to be on the lookout next time I go to Lowe's. I've found myself wanting a Den after seeing that they look like a better version of "lucky bamboo".
(Yeah, with four Phals, I don't exactly have space for another plant, but that's the same thing I thought when I got my first Phal anyway, so...)
I know I have seen at least Dendrobium spectabilis and D. aggregatum as bag babies before. Not sure about other Dendrobiums, but maybe more?
I bought the D. spectabilis that I had seen recently. I don't have many Dens., as I have not yet been able to claim success with the genus. I also have a D. crumenatum which is doing OK, received as a gift from a friend on this site.