Is the use of savestates allowed in full game runs? The rules are not so clear about it.

Sorry about that, the use of savestates are allowed for practice and for level runs. E.g. Starting any level on any save state is valid. However, in a full game run you must start from a game reset and you are not allowed any save states during the run. Hope this helped:))

So loading a savestate that begins immediately after a game reset would invalidate a run?

I can field that one. To answer your question, yes it would invalidate a run (if such a run exists on the board please reach out to one of us for discussion). Since we don't have any deep understanding of how/when RNG becomes active in this game we have to assume that loading a savestate after a reset would have effectively locked in the current RNG seed. This means that the run itself wouldn't be measurable on the same grounds as the other runs, but I agree the wording of the rules should reflect these things. Rahvin & myself can attempt to coordinate this effort and settle the verbiage in the days ahead, but I can only speak for and offer my own time. We will get this settled as soon as possible :)