There is merit in this. I have often been concerned about the air flowing through the vac system. Over here my cars spend much of their life on dusty dirt roads. The old 300D (now parts car) had its vac pump discharge going into the air cleaner. Though I never found any dust in it, I was always concerned about it given how much dust there was accumulated every place on the car.
My newer 300D & the 2.5 both have internal ventilation of the vac pump, so unfiltered air goes into the crankcase. While I have never seen a build up of dust or oily mud, it does concern me. Maybe I will place a filter on the main vac line just before the vac pump & on the small line that also comes out of the pump.

__________________
Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving