I was there yesterday. The merchants would take Ar peso at a very bad rate, but I got a reasonable rate for US dollars. It does seem they much rather have dollars.
It's been that way for the better part of a decade. When it comes to using AR$ in Uruguay, I try to avoid it. For even around PDP, using Argentine or Brazilian currency at retail points is just a waste of money for me relative to a ATM visit or using a no-forex fee credit card. And using the ATM or the credit card, getting stuck with counterfeit notes drops relative to what happens via other retail transactions using cash -- a reason to not use US$ there either.