I often have a little bit of inbreeding in one or other of my matings; with a small flock it’s hard to avoid completely without going to extreme lengths.
My rules are, all about-to-be parents must be excellent specimens. If the tup or his dad has any undesirable features, then I’d try to avoid any inbreeding but at the least, would not use a ewe which had the same undesirable trait.
In general, one would not expect to keep the offspring of such a union for breeding, but on the rare occasion that all the positives line up and non of the negatives, one can get an excellent specimen. If truly exceptional I might keep such, but would be certain to not inbreed it again.