It really depends on what is actually stated in your father's agreement. But in general the answer is no. Your ticket is only valid on the airline that 'marketed' it, not on any codeshare. But that's not to say that an inexperienced or unattentive UA agent wouldn't clear you, but just be careful and don't count on it because you could get stuck on the other side of the pond with no way to get home.

I have been cleared on UA operated LH codeshare flights with a LH ticket but I certainly wasn't suppose to be! Occasionally practical airport application runs contrary to what's stated in the formal agreement.