I agree with Speed on the fact that this strategy would be situational, and if you didn't need to use the strategy, you'd need to waste a slot on Grumpig for Trick, so that you don't poison yourself.
If Breloom doesn't need Thick Fat though, then the strategy's importance is minimal, and Grumpig's moveslot for Skill Swap isn't necessarily useless, but not needed.
It's a complicated one to critique, because I don't know how it would fare in most situations. I'll rate it a 7 though, saying that it's a fair strategy, when deployed under good circumstances.
And no, Badly Poison won't slowly restore more HP with Poison Heal. It just treats every Poison ailment as a regular Poison.