I have one of the new Liliput B-B Gemeinder HOn30/(HOe) locos. It comes with a swinging drawbar and with it can supposedly traverse a 9" radius curve coupled to its train.
Would look funny, but if you need tight curves and the equipment will handle them, why not? Just use good design practices and leave straight zones for coupling. I have no experience with the swinging drawbar, but it should work well on tight curves.
I converted mine to HOn3, although still able to switch back to HOn30 or HOm.
http://cs.trains.com/mrr/f/88/t/215880.aspx
I use it on much broader curves, so removed the drawbar and installed Kadee 714 couplers for compatibility with my other equipment after conversion.