hmmm.... interesting question....
This is assuming that all the oddworld creatures banded to gether against us Earthings, correct?
I would say we have a very strong chance of winning, but Oddworldians could have an advantage in some instances.
I suppose it all depends on the situation, resources, and who will lead us. (I vote Arnold

)
EDIT: on the Nuke note, we may have trouble there. We would first have to see
how the Oddworldians get to us, or if we get to them. If they all of the sudden apppear out of nowhere, and start invading, nukes would be a bad idea because it would create so much radiation, that area would have a very negative effect for anyone who would choose to live there in the future.
If they come, say, through a 2- way "portal" to travel from there to here, a nuke can still be a problem, as I'm sure they would have guards on their side of the "portal". We could use a suicide mission- send a few guys through with sum nukes, then detonate as soon as they pass through- hoping that the guards don't stop them and then use the nukes on use. but if they were to succeed in the suicide mission, there's no telling how much, if any, radiation would seep back through the "portal" and damage the area around it.
it's a very touchy matter. fictional, but touchy.