Consider the implications of why chat rooms are not allowed - it is not feasible to moderate online speech on their platform, and they don't want to deal with abuse.
So I'd say no, you probably do not want chat enabled in your multiplayer game if you want to host it in the Arcade.
On the other hand, I'm not certain they actively check submissions, seems more likely it would get taken down if there were a complaint. A chat functionality would be simple enough to enable or disable with a simple quick update either way.