I've had 4 marriages in my colony now and only the very first used the marriage spot I put outdoors. All subsequent marriages took place in the (rather cramped) dining area. The same happened in my previous colony, which had three marriages.
I would expect the marriage spot to be used for every marriage, or to get rid of itself after the first if it's one-time-use.
They'll reuse it, just not if it's freezing or terrible weather or something.