Theoretically, I don't see why you shouldn't. Most tenders charge at between 1 and 4 amps, and a power outlet for e.g. heated clothing would be good for at least that.
However, I'm just wondering if that socket is ignition-controlled like on my cars, because if it is it won't help you at all. Someone will know.
Personally, I always fit a fused flying lead to my bikes with a weatherseal socket to suit my tender, so it never occurred to me to use the powerlet socket.
Nick