Reporting back on this - the stone sealer clears over time (it was a little cloudy in the pic in the post above) and it does create a water repellent coating on the tiles. But, because the engrave cuts through the top and exposes the internal travertine structure, the engraves don’t seal as well - I expect it’s soaking into the tile and it’s just a matter of how many more coats I’d need.
I did try wetting the tile and no issues on the field but the engrave would leave dye residue on a paper towel used to dry it off. Suggests that the dye is not water safe after only a week of drying.
Since we’ll use them as coasters tomorrow I sprayed them with a couple of coats of Helmsman Spar Urethane in a gloss finish. Home Depot $10/can 
https://www.homedepot.com/p/Minwax-11-5-oz-Clear-Semi-Gloss-Helmsman-Indoor-Outdoor-Spar-Urethane-Aerosol-Spray-33260/100199613
Dried overnight and totally sealed and glossy tile finish. No bleed through of the dye nor does it rub off on a towel when drying the coaster.
Oh, son #3 came back from school and brought many cheeses from NY State to go with snacktime tomorrow. Wife says “you wouldn’t have a cheese board in your collection of lasered ones that we could use would you?” Well, no (just donated a bunch of them to the MakerSpace for their annual holiday crafts & such fundraising sale). But a few minutes in design software and a half hour in the GF and, yes we do 
