Nope - you don't have to be on the trusted list or PM of both profiles, but it does make the merge go more quickly if you are. In essence, the PM of the 1st profile (either can be 1st, so don't get caught up in order) provides approval - the PM of the 2nd profile provides approval and the PM who provides the 2nd approval then completes the merge now that there are 2 approvals on the merge. If you happen to be on both, you can approve #1, approve #2 and then merge pretty much all at once. But either way it gets done once 2 approvals are registered.