before having switched over to underbelly heat i used the black party lights that you are talking about, without any problems from my snakes.
ball pythons dont need the uv rays like some other animals.
***i dont know anything about the keeping of geckos so i can not answer to that.***
my only advise to you if you do choose to use them to look them over very well to make sure there are no small little white spots on the bulb that will let white light through... as this can cause undue stress.
i would also add that same advise if you buy "reptile bulbs" because there is always that chance that the bulb may have that one little flaw so tiny that we would not see it with the bare eye.
and that slightest amount of white light will be enough to stress your animals over time as it would be the same to them as having sun 24-7 to you or me.

just my