Ceremony and reception in the same seats?

My fiancé and I are having our wedding in our backyard. There is limited space for a tent, so I'm looking at renting a 20x30 foot tent. Space is going to be a concern if we are having both the ceremony and reception under the tent. Would it be super tacky to have guests sit in their seats at the tables during the ceremony? This would be a max 30 to 40 guests. I'm pretty set on a tent because the past couple of summers have been pretty rainy, so I don't want everyone to be caught in the rain.