Yes. The operator of a similar platform was subject to an SEC enforcement action because he failed to register with the SEC as a securities dealer.

If you don't want to register, you need to prohibit US customers, and you should probably implement some basic measures like IP geolocation bans to cover yourself legally.

It won't make a difference whether you use bitcoins, USDT, euros, or whatever. These requirements pertain to the service itself, not the type of collateral customers use.