Should I be concerned about racking another piece of gear above my Ampeg SVP-Pro? Are the ventilation ports in the back of the unit sufficient to cool the unit?
You should contact ampeg, but I think you will be ok. I have a QSC with a SVP-CL adn SVP-BSP, no problem at all in a 4 spaces rack
I typically rack my SVP-Pro with no empty spaces above or below. It's not like the vents are completely blocked: there's still a small gap between each module in the rack. IMO, the only thing that might happen is that the chassis will get warmer than usual, and I don't see any danger from that. Note: molded plastic racks such as the SKB Roto Rack typically have corrugated shells. Placing the SVP-Pro in the top space of such a rack will provide a bigger gap on top.