Hello Steven,
Yes, you can do it. It is a supported scenario.
You have to define a join rule on your AD MA1 or 2 or both.
For Example, if you have a strict match on the SamAccountName or any other attributes.
You can also have multiple criteria to join your users.
See this post for understanding what is the join rules in MIM: https://techcommunity.microsoft.com/t5/core-infrastructure-and-security/understanding-joining/ba-p/974576
BR,
Sylvain