Will an agent work outside their genre comfort zone for a current client?

It depends on the agent. Some will take it on, some may refer you elsewhere, or some may set you up with somebody else at the agency to handle that book. It really depends on the agent, how strongly they feel about that book, and if they have any contacts within that genre. Even if they don't handle it, they might have a few contacts that they can use.

What Ryan said.

I also read recently that agents like to know what's going on, so discussing genre, change of genre, career path, next book ideas, etc is encouraged. They want a good relationship with their authors. Communication is the best step that direction.

If you already have two different genre books, and are offered representation, it's a good conversation to have from the beginning.

Nathan Bransford's views on this http://blog.nathanbransford.com/2007/12/genre-hopping.html