Each game, Pokémon, Ingress, pikmon etc. has it’s own rule set on what can go where. However any submission can end up in any game. Even if you submitted through Pokémon Go it doesn’t guarantee it will appear in-game even if accepted
As far as I am aware Pokémon can have 1 only per S2 cell. 1 exception to this rule is sponsored gyms or stops.
I believe ingress can have more as I have seen 2 ingress portals alongside a Pokestop while reviewing. (They are actual portals, I verified them with an ingress player)
From our local area, all present Pokestops are also ingress portals as far as I am aware.
You should be able to find the rules if you Google them or someone here should be able to point you to an explanation as this comes up quite a bit. I think this is the link that may help you:
[Why was my Pokestop/Gym/Portal/Flower/Mushroom (etc) removed?]