So, the Fence Cutting Blades are melee and do not say "fixed front."

So, with an AT-ST if someone gets behind you, could I technically reverse into base contact (making sure to only do a partial move to avoid displacing), and then use my fence cutting blades?

Yup! Had a friend do that to me with his AT-RT the other day.

Just remember that the reverse maneuver is one less speed!

i did this to Vader actually the last time i played and ended up finishing him off.
I donkey-kicked him essentially lol