a. I couldn't find the Low Crawl event in the rulebook. I played it as synonymous with the Stealth event based on the wording on the card (card US-3).
Ooops. Yes, this is synonymous with Stealth - and the wording on the card is correct, the name is an old name.
b. Stealth (and Low Crawl?) allow you to enter enemy occupied hexes? I played that it did since I couldn't find anywhere that stated otherwise.
It specifically states "adjacent" - without qualifying whether it is enemy-occupied or not. You did the right thing.
c. The situation arose where the defender wanted to play Mines into a hex containing a Pillbox. I ruled this illegal since Mines are a "fortification" and only one fortification / hex. I just would like to verify this.
F100.3 rules the situation and you ruled correctly.
d. From the comment at the end of A33 (Ambush), it seems like the active player can play ambushes even if the inactive player totally wiped him out via ambushes.
e. And just to make sure I have this right... it's entirely possible for a broken team to advance into melee and wipe-out a much larger force by throwing down a fistful of Ambush actions.
f. Last one... you can't strafe a tree-line (er, jungle line?) as each hex of jungle creates a blind-spot covering the next hex of jungle?
It operates as an obstacle exactly the way Woods operate. As long as what you mean by "strafing a tree-line" excludes those hexes where you have a direct unobstructed LOS (as you "strafe along - but not through to behind"). If what I'm writing does not "sound right" then we have to go to precise examples to make sure we understand one another.