When the electrician hooked up the power cable from the spa to the GFCI outdoor pony panel he did so by going through a "toonie" sized hole (slightly larger than the size of the cable) in the cabinet to the lower left of the spa motor access door. I don't recall noticing a "knockout" in the cabinet so I am assuming that he drilled this hole himself. 
Two questions: 

1. Was this the way that wiring access was supposed to be gained to the inside of the cabinet? If not, how was it supposed to have been done? I have looked through the owner's manual and it doesn't seem to refer to how the wire should be run, just that it should be done by a certified electrician (which he was).
2. Regardless of the answer to question 1, what's done is done. Will this hole affect the insulation properties of the Heatlock system? Should I be attempting to somehow fill/insulate around cable/hole?

Answer: 
We don't designate an area for electrical connection through the wall of the spa because it is a different location in every application. Your electrician followed a standard method for bringing in the power and a properly sized hole will not affect the insulation efficiency of your tub. However, it is a good idea to fill the gap with fiberglass or foam insulation. Fiberglass can just be stuffed into the hole with a pencil or popsicle stick. If you use expandable foam, applied from either inside or outside, remember that it expands considerably; don't try to fill the hole completely-- a tiny squirt is more than enough!