I loved the Dole Whip with Rum that we had at Epcot during the Flower Garden show last year. Normally I don't "love" Dole Whips but the rum made it super yummy!
Nope. You can never use dining credits to purchase alcoholic beverages (with the single exception of the dinner shows, which include wine and beer in the price)
The "bad" reviews I have seen were from those who expected something else (they thought the rum would be mixed in with the frozen beverage but instead it is poured over the top of it.)