I think a 17 year old is old enough to decide she wants to be involved with him, and on an absolute moral level I don't have an absolute problem with it, however it does may me think you EX is mentally unstable in some way, especially as you mention he has no job etc.

Is he 25, is that right?

It is somewhat dodgy I admit, I mean he is on the absolute cutoff limit for me. Where I live 17 is age of consent, so if she was younger I would call the police!

If he is older than 25 then that is even more dodgy, and even more concerning.

If he is 25 and has there is absolutely no signs of any form of abuse or seriously inappropriate behavior then I would probably let is slide somewhat myself..