I don't think the term "guthook" is really appropriate either. It gets used a lot to describe the curved detent on the back of skinning blades that is sharpened along the inside radius, allowing the knife to cut through the hide without risk of puncturing/cutting into the paunch of an animal. I call that a "zipper" feature. A guthook is more descriptive of the unsharpened hooked probe commonly found as a second tool on folding knives used for dressing birds. The hook is used to reach into the body cavity and extract the innards of the bird whereby they are more easily separated and removed. Without a guthook, dressing a bird can be tedius and often messy.

A zipper edge on a skinning knife is pretty handy, but a skilled hunter can readily use the tip of his hunting blade and the index and middle fingers of his off hand to do the same task. Once a slit is made in the hide, it is pretty easy to slip the two fingers underneath and ride the tip in between the fingers and at an angle so the blade edge will sever the hide as it is drug along a line with the fingers guiding it along. Done properly, the risk of overpenetration is insignificant.

My general rule is if you have the zipper edge on a knife at hand, then use it. If not, then make do with what you have and don't fret too much. It ain't rocket science. Just take your time and do a good job.