A friend and I was toying around with this just yesterday, as a matter of fact. From various tests, adding a person (and them adding you) to your friend list (or by default) does not allow you to share sensors with them.
“Member A has the owner of Member B's ship, vehicle or station on their friends list and Member B has the owner of Member A's ship, vehicle or station on their friends list.
- 2.3/ Sharing Sensors ”
While the rules state that what we attempted should allow us to share sensors, it did not register as such when using a scan. ( There was no little dish next to the ship itself, indicating that we would be sharing sensors). Unless we were doing something wrong, I think that there may be a bug involved.
I've shared sensors with other factions on many occasions, when they are on our friends as we (presumably) are on theirs. Remember it goes by ship owner as to if they will let you use their sensors, not pilot. Also check your character IFF settings, as faction settings will override your personal choices.