I'm going with others and saying your doc is wrong (no I ain't a doc but been swimming and diving for ages). If you had a neck issue, yeah snorkel. If not it's not going to help, it's only going to make it worse.

And seconding the issue of being in OW with one unless you are not near anyone and it's glass flat. I recently joined a swim program that uses snorkels often, and swam for the first time last weekend with one. There were a few lengths when I had to figure out whether I stop or could I get to the wall as it was full of water. Either through chop, or more often my habit of turning my head even though I didn't need to.. introducing water.

I guess just saying even without lung problems unless you practice quite a bit snorkel in a race is going to introduce ay more issues than it solves

As for how i'd feel if you showed up, wouldn't really care.