That approach will improve the filtration compared to nothing, but you need to be concerned with what size dust particles it will filter out and how much air it can pass. That crank case vent ad does not specify what size dust it will filter out. I'm not saying that it will not filter out the adequate size, I'm just saying you don' know. The McMaster-Carr filter claims it will filter out anything bigger than 10 microns...that's 0.0004 inches and larger...that's very small. The next thing is how much air it can pass. The McMaster filter spec is 10 CFM at 100 psi where the vent has no spec. Once again, the vent may be fine, but you don't know. I was unsure of how much air the McMC filter would pass at our low pressures (5-20 psi) so I bought it and did an amp draw test with, and without, the McMC filter and found it to be minimal and I accepted it. Ideally, the filter should be large enough to easily pass air without any noticeable amp draw increase.

The most important unknown is the particle size that the vent will filter out. The air flow can be determined adequate with an amp meter test, but you can not easily determine the micron rating. The smaller the micron rating, the bigger the filter will need to be to pass more air volume.

Fish on!,
Noel