it is actually against US law for americans to spend money in cuba, but you can legally go there. silly, but true. and they do fine people for breaking that law. if you ever want to work for the usg or a contractor, it is wise not to go as a tourist since it is impossible not to spend money on cheap rum at least..... there is a US diplomatic presence in cuba, so you can bet that the USG knows exactly who is visiting, even on another passport......