Does anyone know/have any resources on how to sew snaps into rope seamlessly. The only place I have found is in the original Tarbell lessons where they explain how to sew the snaps in, but it is rather vague, and when I have tried it as they instructed, the seam is horribly obvious.

Frankly, I don't think it's possible. Especially without a seam.
Magnets or screw gimmicks for the smallest seam.

The Pavel Walking Knot routine used snaps very effectively although I have NO idea how they were installed. If I were forced to do it, (I’m sure it’s a VERY long process) I would try cutting about 3” of the core out of the rope and unraveling the outer sheath down too to that point. Maybe try wrapping some tape around the rope at the core cut line to hold everything in place . I would count the number of holes in the snap then divide that among the number of unraveled rope strands. Splay out the strands and place the snap in the center against the core. Take a large eyed darning needle threaded with a single strand of the sheath and go down through the snap hole into the core an inch or so then out the side of the sheath. Continue a few more stitches through the core and out the other side to hold it in place then repeat with all the other strands until it is secure. Good Luck!

In addition to Ray's advice, try using Fabric glue, available in craft shops. Designed to use on fabric, it remains flexible.