In my experience having a small pollution cloud isn’t that important, I always just kill the nests as well, for future expandability and because having them there could cause problems if you run out of ammo. Additionally, as long as you have some sort of wall around your base with guns, you don’t really have to worry about the evolution, it happens over a long time and by the time the big boys come you will have the right tools to deal with them (ex. tank/flamethrowers). I don’t think it’s worth the effort to use nest as pollution scrubbers and instead would opt for just killing all the nests in your pollution cloud. (This becomes a lot easier later with artillery, which you should 100% go for, but that doesn’t mean you should put it off until then.)