I was comped from US Gold to UA Prem Ex in Dec, 2003. The alliance was already in place, but things may have changed. I think anti-poaching would be formalized within *A when US joins.
The speed of matching was suprising. I faxed in my US statement late in the evening. The next afternoon I checked my UA account and I was Prem Ex. It may have helped that I was already UA Prem with 40+ k elite miles in my account.