Yes, and in the case of DCC you'd get hit from both ends if using a Travelex card.

I still maintain in the US that DCC cases are likely few and far between and easily avoidable when encountered, but I have no way of testing this short of having my wife use her Bank of Taiwan Visa debit card. However, while she has helped me completely dodge DCC successfully in Taiwan, she's not that interested in trying out her card just for the sake of trying it out. She let me make one small purchase at the Books Kinokuniya, which didn't have DCC. On an unrelated note, I was impressed with BoT's currency exchange fee on the posted transaction amount.

The reason I say that DCC cases are easily avoided is that at almost all big box retailers there is an electronic signature pad facing the customer. DCC, if offered, would likely appear as a choice on this signature pad. I imagine it would be just like the DFS setup we've seen at HKIA, Guam, and SFO. I could see two places where it could be problematic. The first is at hotels because many use an easy checkout system where the night clerk will slip the bill under your room door in the early hours on the day of your departure. However, I think a visit to the front desk would be able to rectify any DCC attempts. The second is at restaurants. I would think in this case that bringing over the manager or asking the waitstaff to void the transaction and rerun it opting out of DCC would do the trick. The tipping culture in the US would motivate the restaurant staff to want to do the right thing.

Above all else, I think the customer service oriented training at most establishments would prevail, allowing for a successful opt out of DCC. I've read reports here where some establishments overseas seem to know exactly what they're doing with respect to DCC and attempt to swindle the customer with lines of, "We'll see what happens..." or "There's no option to disable it if you use a foreign card." DCC here would most likely be met with looks of confusion and curiosity. For instance, I doubt that the waitstaff at the Outback Steakhouse in Merrillville, IN have ever seen a non-USD denominated credit card.