I can't speak at all to the Wal-Mart portion, but I use this card for online donations and do the redemption portion every month or two It is a two part process (redeem cc to paypal account, transfer from paypal to bank account), but it's fairly straightforward and I don't believe I've run into a minimum redemption limit.
General caveat, paypal doesn't have the greatest reputation as far as how they treat their account holders which is why I don't leave any money with them and try to remember to collect the cashback quickly rather than let it build up...if they decide to lock any portion of my account, I don't want anything owed to me tied up with them.