Anyone have any understanding of how/what these two stats do for PVP?

How they effect things like roots/debuffs and damage?

Spell pen reduces your targets resistances to your spells. The only class that will have any sort of arcane / nature resist in pvp will be demonology warlocks (unless for some random ass reason someone is actually wearing resist gear...)

Spell hit increases the chance that your spells land. I believe the cap for PvP is around 2%