Does -esque need a hyphen? No, the hyphen is optional. And don't worry if your spelling checker puts a red squiggly line under your novel -esque words. The alert lets you know that the word isn't in the spelling checker's dictionary; that doesn't mean it's wrong.

Is esque a valid Scrabble word?

ESQUE is not a valid scrabble word.

When should a hyphen be used?

Generally, you need the hyphen only if the two words are functioning together as an adjective before the noun they're describing. If the noun comes first, leave the hyphen out. This wall is load bearing.