Well, moltres isn't truly a roaming pokemon, it's a stationary I believe. You maybe don't walk up to it and hit A, but it still has a specific encounter area (the cave area, Sea Spirits Den I believeits called :]). I guess you could consider it a roamer. But whether its a roamer or not doesnt matter as synchronizing definitely still works :]. If it didnt, it would be hell trying to catch a good nature bird with proper ivs.
Edit: it's technically a roamer the times you encounter it in the wild, but after it settles in Sea Spirits Den I would assume it is classified as a stationary. However, like I said up there, this info matters not one bit. Synchronizing is definitely possible on it no matter what :3
Moltres is a stationary Pokemon when you become able to capture it.
Really?! Well, that's good to know. Cause I was wondering if it was possible that synchronizers would still work on moltres and the iv set can change still (even though the roamers on HG/SS don't (Like Raikou and Entei)). And it seems that I got my answer. ;)