the only issue being that it is above the voltage specified for a NEMA 5-15?
Sorry for the long answer. No doubt you and the OP already know most of this.
US domestic power is split phase with two hots and a neutral. Either hot to neutral is 120V. Hot to hot is 240V. Like the UK, modern US sockets have a safety ground. Neutral is tied to ground at the breaker box. There are ground fault interupters (GFI), but that is done differently than the UK RCD / RCBO.
Nema 10-30 is the old hot,hot,neutral dryer socket. There is no ground. There is no fault detection. A UK style RCBO won't work because the neutral is meant to carry current. 10-30 is not used anymore but there are plenty around in old houses.
There are cheat 240V adapters. I would't use one. I doubt you can get one at home depot.
Unsafe because:
- Somone could plug a 120V device into the 5-15 socket. Boom and worse, becuase....
- No ground connected to the ground pin of the 5-15.
- If the ground pin on the 5-15 is connected to neutral on the 10-30, the ground pin could be well above ground potential. Oooof
- No GFI
- 5-15 isn't rated for 240V.
- The insulation on the wires connected to a 5-15 plug don't need to be rated for 240V. They might be but who knows.
The 5-15 is rated to 15Amps and the 10-30 is 30A. That's ok, but if you've got a 30A circuit, why not use it?