If it's a 5 bolt hub, one missing lug isn't going to be that crucial, so long as the other four are torqued properly.
The balancer you're referring to is a 'bubble balancer.' Basically, the wheel is balanced on a center point, and weight is added opposite to the side that dips down. When it's balanced, the wheel will sit level. It's not a bad tool if you know how to use it, but it only does a 'static' balance- it corrects for radial imbalance. A 'dynamic' balance uses weights on both the inside and outside of the wheel to also correct for lateral imbalance.
A static balance is usually good enough to eliminate most if not all vibration up to a reasonable speed. Just don't expect a super smooth ride at 95mph.