"Stealth tethering" isn't required for Sprint. You can't really stealth it anyway, it all shows up as data over the phone. Now if they actually look at what you're doing - it'll be obvious you're tethering.

They won't do anything about it though. I regularly go over 5GB to no ill effect. Sprint treats me well. As long as you're not abusing their network too terribly, they tend to let it slide.