Great. A follow-on question, then. When attacking the frame with one white in a hazard area, does it activate?
P91 says: When one mobile frame attacks a mobile frame that hasn’t taken its turn yet, switch to combat order. But p101 says: If it doesn't have a defense number, switch to combat order. Those are two distinct conditions. The difference between these never matters without hazardous terrain, (and equally never matters with CmdrRook's house rule,) but in this situation there is a frame that has not yet taken its turn but DOES have a known defense number. The question boils down to the intent of the rule being to primarily find the defense number (and activation is just a necessary result) or primarily to activate the defending frame (allowing the defender to react)?
I'm leaning toward activating the frame. (but I'd house rule it that if the frame has no SSRs then the attacker does not need to wait for the defender to roll. The defender cannot declare a target and rolling will not affect the incoming attack at all. Because it's undefended, it's likely to be destroyed and its rolling can be skipped if it is. If it survives the attack, it activates next and can roll and move.)
On a completely separate line of thought, perhaps it makes sense to penalize a one-white frame in a hazard with losing their free green instead of the white. That drops this whole question, and might be a tiny bit more fair to the poor sod.