That got me a bit confused. In the Core Rulebook, the Oath-taking section's last sentence states, that "in addition to the listed Codex Squad Mode abilities the Kill-team will also have access to their leader's Chapter Squad Mode abilities" - we took it to mean that the leader's activated chapter squad modes can be joined by the team.
Alternatively it could mean, that if we have, say, an Ultramarine leader, he can activate Lead by example, but it cannot be joined by others if the'yre not smurfs, while Armour of Faith (the other guy is a Black Templar) cannot be activated at all, since he is not the leader.
Since the group is pretty new, and I took up GM-ing Deathwatch only recently, there has been only a very light use of squad modes (I scaled down the enemies a bit to familiarize ourselves with the combat mechanics first, and also because the kill team consists of only two SMs). Anyway, I'd appreciate if you could help me clear up the confusion before Squad Modes become the deciding factor.