From what I've discovered; oxygen is filled into welding tanks and medical tanks using the same master system, same oxygen, same everything. The difference is when it leaves the filling plant - chain of custody (and tank configuration) is what really separates "medical-grade" and "welding-grade" oxygen.
No matter the source of the tank or oxygen, I'll still feel better with medical-grade regulators and flow meters - just "feels" more sanitary to me.