No, I think Suran had most of the military behind him. After the coup, we didn't see any Romulans fighting against the takeover -- not until later when it became clear that Shinzon was betraying them. Yes, the military nominally answered to the Senate, but that doesn't mean they couldn't plan treachery behind the Senate's back. History has its share of examples of militaries overthrowing their own governments. A well-known recent example was the 1999 Pakistan coup where the Pakistan Army and its chief of staff General Pervez Musharraf bloodlessly overthrew the elected government and instituted martial law.