Well obviously I don't speak for mIRC Co., but I see no reason why any software developers would have an issue with WINE (besides Microsoft of course). It immediately provides a massive user base for their product without having to do any additional work themselves. Personally I think it's fine to use software with WINE or any other emulator/abstraction layer unless the EULA explicitly states otherwise.

Spelling mistakes, grammatical errors, and stupid comments are intentional.