I have two engines with a vac pump, neither of the valve covers has a baffle for the vac line. The amount of oil drawn through is negligible, I get more water in the catch can than oil and it isn't a lot. If I do start to get oil in the can I check for a leak, rocker cover gaskets, loose fittings etc. As has been stated, if the engine is sealed well and the vac relief valve (if used) is in the correct position you should draw very little oil.