I don't think it's uncommon for agencies to pass along your file to an attorney that they have had success with before. If there is no exchange of money between the attorney and the agency, that should be fine. But, like Traci said, you definitely may chose a different ART/ surrogacy experienced attorney if you prefer.
Regarding escrow, is the attorney licensed and bonded? Does the agency have access to the account? Are you doing a set monthly stipend or reimbursing for actual expenses as they are incurred?
I would think having the surrogacy agency look over expense reports to make sure everything is legit before sending the request to the escrow agent is a nice value add. A set monthly stipend instead of receipts for all vitamins and pregnancy supplies is a nice way to keep the books clean. Again, you should have the right to pick any escrow agent, and the surrogacy agency should not have access to the account.