Sorry Thal, I mispoke. When I said "NO units should have 'see invisible' subs" I was referring to the promotion PROMOTION_SEE_INVISIBLE_SUBMARINE.
Yes, any unit ADJACENT to an invisible unit (such as a sub or anything else you make invisible) can see it, and that is appropriate.
Mentos, in his Unity Mod, had anti-aircraft & anti-tank units invisible. You had to get up close & personal in order to spot or attack them.