Yes, they can. The good news is that not all snakes have fangs strong enough to go through rubber boots.

Do wellies protect from snake bites?

Rubber Boots – Rattlesnake Protection by Type

Gardening Boots — these provide minimal, if any rattlesnake bite protection. ... Rain boots (aka galoshes or wellies) — the typical soft silicon rubber rain boots, galoshes or wellies don't provide much rattlesnake bite protection, although they are better than low top shoes.

What kind of boots protect against snake bites?