I had the same suggestion made to me during some remodeling work that
required a bath fan to be re-routed. I think as long as you get the
duct into the roof fan opening, it will work.

However, I came up with what I think is a real problem. In the
summer, the attic fan will be running. That will create a vacuum that
will draw cool inside air up from the bathroom and pump it outside,
whether the bathroom fan is running or not. This could be a
considerable energy loss.

The best solution is to put in either a roof or soffit vent for the
outlet. They are cheap and easy to do. The condo association can't
stop you from fixing this the right way. If necessary, just bring in
the local code enforcement officer.