I know that when they had the last P&G deal at Walmart (Think it was spend $30 get $10 GC) you were able to use coupons against your purchase. They are looking for the fact that you purchased the product for whatever amount, not how much you saved in coupons afterward.
I wasn't going to try this deal, but went to WM today and found a pkg deal of Pantene Shampoo, Conditioner & a free hairspray on clearance for $5 - they let me use the 2/$2.50 coupon - one on each pkg!! Then I bought one of the Venus giftpacks for my mom ($14.98 - $4 coupon) and one of the Gilette men's giftpacks for my husband ($14.98 - $5 coupon) and two packages of the Pantene shampoo ($10 total - $5 coupons total) - so, so far I have $39.96 toward the $50, but only spent $25.96, plus once I spend another $10.04 (which will definitely have coupons applied toward it!!), then I will at the most have spent $16 plus tax ($16 is if I don't use any more coupons). What a sweet deal!!! I'm sure I had a goofy grin on my face the whole way out to my car!!! (I also got some of the Tylenol and Stayfree deals too). What a day!! :)