if a certain massage parlor (not an AMP) has numerous positive reviews on TER can one rest at least a little easier that it is safe from LE?

Positive reviews are a good sign.

Yes, while positive reviews are a good sign, nothing is 100% safe. For all you know, that place has been under surveillance for months.
That's why I always go with well reviewed independent ladies, whether its just for a massage or for a full GFE session. Agencies and parlors make me uneasy for the very reason you described. Good luck.