I would say yes, as long as you FULLY disclose the history to potential new owners. I have been in the situation of not knowing the genetics of my geckos, and it is not fun.
I'm not sure if the issue for you is that you don't know the gecko's genetics, or that you're worried about breeding a gecko to its mother.
If you're concerned about its genetics: is there any way to tell which female he came from based on test breeding? If so, you should do that, or else tell a prospective buyer of his offspring about all the possibilities of his genetics based on the females you can't eleminate as not being his mother
If you're concerned about breeding a gecko back to the parent: as long as this isn't done generation after generation, this is generally OK to do with geckos and is done quite commonly.