Just added this to the wiki, but I've been paying my Citi balances with a UFB Direct since the middle of 2014, and haven't had issues. Just have to make sure to stay under the $1500 daily limit from UFB for debit transactions.
On the flip side, I can't tell if I'm actually earning points for all this. I mainly only do citi payments and Serve loads using my UFB, and I seem to get some AA miles from UFB each month, so there's some evidence that I seem to be earning some AA miles from this.