The basic rule book says that stealth prevents your opponents declaring the stealthed characters as defenders

Assuming there has not been any change, this means I can still declare those characters on the attacking side, if they have naval enhancement?

(I have a reason for wanting to do this!)

Stealth says you "cannot defend," so it's a little more than just being unable to declare the stealthed character as a defender.

But yes, there is nothing stopping them from being declared as an attacker with Naval - should you need to fuel "lose by 4" effects or "participating character" effects.