Oanda is actually registered NFA and with the CFTC, RFED, and FDM. They're very beholden to the regulatory scrutiny of America. Do you mean for dealers offering other securities than forex?
It's obvious U.S. is not the ideal place for Forex traders in general. That's why gave up moving to U.S. My FX broker is Switzerland based Dukascopy and I am very satisfied.......
That's why I turned to non-US based fx brokers like Tickmill, Exness or Hotforex. FCA regulation, I guess, is a decent substitution to legal safety that offer brokers in US, while their deposit and other requirements are much more flexible