SBD is for 'scout, bomber', 'D' was letter code for Douglas. The Vought have had letter code 'U' (like in F4U), Grumman was 'F' (like in F4F), North American was 'J' (like in FJ). As you've guessed it, if the 1st letter was 'F', the aircraft was in fighter class (or VF class).
Every slow bomber (and other A/C) was vulnerable to fighters, whether it was a dive bomber, 'level' bomber or torpedo bomber.
BTW, what happened to the Stug's pictures??