Groomsmen (the men in the wedding party who escort bridesmaids) and ushers — the people (usually guys) who seat guests — are not necessarily one in the same. They certainly can be, but they don’t have to be. You can still have ushers without having groomsmen (one for every 50 guests is the norm) who don’t stand at the altar during the ceremony, but rather sit toward the back and see that any late stragglers find a seat. They can wear whatever your best man is wearing (such as a tux), but they can also wear a nice suit — so long as they fit with your wedding style.
by The Knot