Share spells

[Renen]

Can a master use share spells to buff his familiar with spells that are only usable on things like undead?

[Chronos]

Yes, if the master (or the familiar itself) is undead, but not otherwise.

[Necroticplague]

Depends on the exact nature of the limitation. If the limitation comes from its "target" line (I.e.:"target:one undead creature"), then the master can get around it by targeting himself, and sharing it with the familiar, assuming the master is undead.