I don't remember seeing this in the FAQ, and did a quick search through it and didn't find anything. But are bombs considered secondary weapons. Specifically regarding the munitions failure crit?

No.

http://xwing-miniatures.wikia.com/wiki/Category:Bombs

no. it was FAQ'd

Rulebook page 19: 'Secondary weapon cards show the header “ attack: ” ...'

Bombs do not have that header. Therefore they are not secondary weapons.

Also I'm pretty sure somewhere on the Using Bombs card it explicitly states they are not counted as secondary weapons.