With most yagi antennas you will find the elements connected to the metal boom and the boom connected to the metal mast and tower... this makes sense for lightning purposes. The tower is normally grounded and keeps the potential problem outside!
This is one of the best reasons for using the gamma match.
Now you can design a yagi with an insulated boom and elements, but why?
Not just lightning protection, which may or may not work depending upon the type and duration of strike, but DC grounded antenna elements are also useful for bleeding off static charges that can make undesirable NOISE on the received signal.
The yagi would work pretty much the same with Gamma Match located on either side of the boom.
It is imperative that you don't attempt to analyze the antenna element situation as a simp;le DC path, often it is not the case. Since your RF is basically AC at some high frequency, the Gamma Match actually is acting as a transformer (autoformer) within a specified frequency band. The whole thing is at DC ground potential, but at the specified frequency of operation, it appears as a nominal load to the RF device attached to it.