The belly in that hotside vent hose will hold a fair amount of oil eventually.

I'm curious if having that vacuum line on the front of the filter actually generates any vacuum
I doubt it

Entirely dependent on the filter and how much air is being consumed. I've seen some with as bad as a 2 or 3 PSI pressure differential across the element.

Just a note for others reading though... if you route lines like these to a vacuum source with check valves, now you have nowhere for blow by to go when you need venting most while in boost.

So, when I run my hot side valve cover port to the air filter like that, it is basically instead of a small filter. Just a source of clean air, and somewhere for excessive boost blow-by to go when my check valve is closed.