Many plain old video baluns aren't baluns at all, but just adaptors that connect the hot to one lead of a CAT pair, and ground to the other one. Any such "balun" shows zero resistance from ground to ground.

The whole idea "bal-un" is to convert from a BALanced signal to an UNbalanced signal, hence the name (and hence not pronounced baylun). The simplest method of doing this is to use a transformer; suddenly ground isolation is probably built in, as it's easier to make a transformer with separate primary and secondary windings.

Which of the baluns you've used give you ground isolation? This is a really worthwhile thing to know, as having ground isolation means fewer possibilities of ground loops.