The area 51 IT Management proposal was floated at about the same time as this one, but hasn't yet made it out of the "define" phase. Based on the discussions here, the IT Management community feels their management issues are different enough. For them PM is a tiny subset of IT Management, although frankly, all of their reasons appear to smell a lot like project management to me. That said, the poor guy who floated the merge question got down voted a lot.
Is it a bad thing to try it out? Instead of asking if it's okay, I'd suggest just trying a few questions to see how it goes. If the questions seem too "off-topic" then we can close them.
The best way to determine if they'll fit pm.stackexchange is to just give it a shot.
The nice thing about StackExchange is that tags can be used to organize questions. If IT Management questions are tagged as "IT Management", then this could help organize the content and separate the questions for users not interested in IT Management while still unifying the site for users who are interested in both.