You are correct that RLT units don’t emit light in the UV spectrum. The fact that the shade # 5 glasses also block UV light I don’t see as an issue, for RLT users. Typically an RLT session runs around 15 minutes. The glasses are inexpensive, around $10.00 USD.
The reason for the #5 shades, is that the IR radiation from the RLT unit can be much higher than the IR radiation to the eye from walking around in the sunlight.
If you have a different application, a different type of glass may be more suitable. For instance, I wouldn’t wear #5 shades to the beach.