We've met a few Danes that slobbered loads... but I'm guessing St Bernards slobber a fair amount more - or do they?
I think it depends on the dog aswell. Great Danes are an ultimate favourite breed. And I WILL own one one day.
It's possible that (apart from the reasons already given why the vets won't spay the St Bernard) they are prone to heart problems and don't cope well with a GA. Most of the ones I've come across seem to have permanently wet chins almost to the point of looking sore.