But the Ferengi were ostensibly neutral in the conflict, and gold-pressed latinum is their currency, not the Federation's. The Dominion are bad guys, but they'll honor treaties and agreements for as long as it suits them. In this case, why would antagonizing the Ferengi be useful, except to drive them into the Federation Alliance?
Perhaps outright counterfeiting might not be wise, but I don't think that it would be unbelievable if the Dominion did some creative speculation. Latinum may have been minted by the Ferengi, but it operated as a global currency (even for the Federation, as much as it needed one). Imagine if the Federation's reserves of GPS were found to be compromised. That might ruin relations with a number of worlds. Were the Federation's allies also cashless societies? Their war effort might have been hampered.