Sounds to me like they don't know much about wheels and tires. I balance trailer wheels all the time. The only time I won't balance a trailer wheel is if it's going on a boat trailer, it's illegal to use lead wheigths on a boat trailer.
As far as 6 lug wheels, you should be able to find stock appearing wheels without a whole lot of issue.
sounds reasonable. so just to be clear: in your opinion, as long as the trailer wheel has the right look, dimensions and capacity, it could be worth trying as a 1/2-ton wheel?