Can you lifesteal off the 3% max health of blood razor?

It adds physical damage.. So I would say yes. However, don't take my word for it. Rito can be quite unpredictable when it comes to the finer points of details like that.

It's bonus physical damage on-hit, which to me suggests that it would simply be applying additional damage to your on hit abilities and auto attacks. So I would think, yes lifesteal should work.

If not, it is physical damage so at the very least and should work with it.