A while ago, i was diagnosing my vacuum system, and ran smoke in the manifold- it came out of my empty catch can.Is that normal?

its this one and the smoke came out from the crevices.

 

yes. if not that equals vacuum leak. my cheapo catch can has rubber or paper gaskets on all sealing surfaces.

 

Yes. Adding an OCC should be transparent to the emissions routing. That is, it shouldn't change the flow or vacuum.
I can't tell if the smoke came from your hose connections or the joints of the actual OCC, but you should modify it so it seals 100%.

 

Catch can should definitely be airtight if it's being sucked back into the intake.