They claim to have the USD in a bank somewhere which means the US can come after them. This is why Wells Fargo dumped them (which is saying something!).
If they hold it as hard cash, practically, sure. If they want to be allowed to send or receive wires and generally not get sanctioned by the United States, no. The U.S. Treasury claims international jurisdiction over U.S. dollars [1].
[1] https://cblr.columbia.edu/the-u-s-jurisdiction-over-transfer...