I probably wouldn't because you'd be able to hear the gate kick on and off, and it would sound weird. I also like to use minimalist drum mic techniques and overdub drums without any other sounds in the room, so there's always bleed between the mics, but it's still effective and doesn't involve other instruments.
I used to try and gate out unwanted snare rattle and stuff - but that was back when I submixed it all down to 1 track going to my cassette 4 track.
defintly do it after.
Well, when my friend was gating the drums for a quick demo he did everything and it did affect the sound. Is it unnecessary to gate that much of the drums?
Yes. It's unnecessary. If there's a serious problem with crossbleed try using fewer mics - one kick, one snare and stereo overheads. It'll be easier to mix and probably sound better - and certainly more natural - too.