Summit's cams are made by Crane. Check any cam specs that Summit lists and you'll find an identical cam listed in Crane's catalog. There are a few cams that Summit carries that Crane doen't catalog, but not many.
The lifters are all made by 2-3 companies that every cam maker in the USA sells with their cams, and none of them are made overseas. Summit lifters are identical to Crane, Comp Cams, and many others.