I have sand in a 10 G with a small whisper HOB. Doesn't seem to bother the filter. Occasionally(about every 6 mos) I rinse the filter it's self as well as the media with tank water, you can even use a turkey baster to shoot water down where the impeller is to clean it.
There is sand in a 30 G long and have an aquaclear HOB.
In about two weeks the 55G will have sand and a penguin HOB all are cleaned as above.
Since i ran my filters it took about 2 days to clear up

my sponge filters are all in bare-bottom breeder and fry tanks

Watch your Ammonia really close, even though the betta breathes air the ammonia will still burn his gills if it gets too high.
Hope that helps.
Carol