Well he only has 2 fights under his belt so i think that throwing him in against a veteran and hall of famer is definately too big a step up. That said Heath Herring is a veteran himself and i expect him to be a good challenge for Brock.
I'd like to see Lesnar in with a striker. If you want to go the easy route, give him Sanchez. If the UFC really wants to test him, give him Kongo. I just don't think Herring deserves to play gatekeeper at this point, and I don't think Lesnar needs to be taking on a well-rounded veteran at this point in his career. It's silly match making, just like putting Brock in with Mir.
I think Brock will win, but Herring is a great test I think. Herring has a history of beating big, strong wrestlers, more accomplished wrestlers than Brock. He's beaten both Mark Kerr and Tom Erikson, although he needed a standup from the ref to get to Erikson. So Herring has proven himself against very good approximations of Lesnar, and if Lesnar can do what those two could not, it will say alot about him.