What HopelessN00b said. I've supported some truly horrible applications. Not horrible from the end-user standpoint--they did the task the end-user needed them to do, sometimes quite well--horrible in the sense that they were poorly coded to need more privileges than they should, or horrible in the sense that they had horrible, poorly-built installers. We were stuck with them because it was a niche application.
In particular, some disability support software does not work and play well with others, and/or has some bizarre and obnoxious licensing method. When I worked at a college, we were legally required to provide access to students with disabilities. Also, things that you would look at and think, "Yeah, they have a small market share," also tend to have twitchy installers and weird permissions--like software to manage student logins in a college computer lab. At one point, our print management software would cause a the client to boot into a BSOD until you booted into safe mode and applied a patch--this was a stated, known, normal part of the install. And don't get me started on the server install of the same product where the server BSODing was a normal part of the install, depending on your OS.
So no, we don't support [insert name of niche application here], but we do support "my business requires this horrible crappy software; how do I get this crappy code to actually function in my environment?"
IMHO, of course.