Maybe your vets getting confused with bearded dragon and Ball python?

Anyway, A megaray would not work in a tub that is for snakes, regardless of species inside.

In general, Mega-rays are the best and strongest UVB lights on the market, And would be a little much for a snake even if they do need UVB.

Also a Megaray depending on wattage needs to be at least 12" from the spot on lowest wattage so its not to high UVB output. So if your using a tall tub, maybe.

Again lights tend to dry up the air so it may solve one problem, create another.

And also you dont want it on 24/7, so at night it wouldnt do any good.

As for snakes with UVB, ive read multiple sources saying its possibly benificial, but none really that says its needed as it is for other reptiles. If so, a snake would only receive it late afternoon, early morning, so the levels would be very low, equivilent to a tube UVB light, not a Megaray which is stronger then the florida sunshine. Anyway, ive read they are finding different "nocturnal species" bask dusk and dawn, and do use UVB, a mega-ray would be overkill and stress the snake out, even if it did need it.

I would assume it is useful, I mean even humans benifit from it, but snakes are not in a manner where its do or die.

Heat pads are great for snakes. A good UTH will do the job, and if ambient are way to low maybe a CHE, As for heat pads, zoo-med are trusty, and then a simple thermostat, and your good.