I don’t know so much about the topic, but my guess is that it is only a serious genetic concern if either:
1) there is a lot of in-breeding in the family as opposed to a one-time thing of a cousin marrying another cousin.
2. There is a known history of an inherited condition in the family.
I would guess that if it’s a healthy family and a one-time thing, it’s not likely to be a problem. But that is just a guess.
Fact is that often people marry unrelated people and have a lot of kids with inherited conditions, so the question is if it’s statistically much, much more likely in this case. If it’s only a bit more likely, I wouldn’t think thats a reason not to do it.