Sorry no info on the Wal-Mart pre-paid cards but...
I am about to go buy a visa Netspend card and see if that works for Bovada, some people say it works some say it doesnt... So im just going to try it out for myself. Wish me luck!
I used the Walmart card on Bovada a few months ago and had no problems, but maybe something has changed. I've had good luck with it on a few different sites.