I don't know about N9, but I think it's just like N900 in this respect.

Although N900 doesn't support J2ME out of the box. there is MicroEmulator, which is available on the repositories. This can run a few J2ME applications

Note that ME will not necessarily run all types of midlets. I have successfully used a number of them, and have had only one or two fail.

I should assume that porting some jvm to the N9 will be possible, unless, of course, there is restriction from security features in the N9