Yes, if they have never been used anally or are of a material that can be sterilized, and then the toy is sterilized.

Using anal beads vaginally without proper cleaning is HIGHLY unadvised.

Sure, but, I'm not sure what the draw would be.

It'd be more pleasurable to use kegel exercisers like Smart Balls that have an inner ball that shakes around.

What Delicious said about the material. If it's a porous material, like Jelly or a silicone blend, rather than 100% silicone, then, imo, it's only safe if they have never been used anally. (Or better yet, get them in silicone from the start. I just replaced my last jelly toy, a length of beads, with a length of silicone beads.)

If they are nonporous and not been used in this particular session anally, (and thoroughly washed after the last session) then they might be OK for some people. Some beads are "pokey" on the ends and they could spear your cervix, so you do have to be careful. They are also more difficult to control once in the vagina, due to not being as rigid as most vibrators and dildos. Also, some beads are 10 inches long, longer than the average vaginal canal. Use common sense, and don't use porous material if they have been used anally.