What a pity - it never is.
Makes for a good enough approximation for most simulations, though.
No it's not!
Unless perhaps the only use you ever make of transmission line dynamics
is for simple narrow band ham radio problems!
Try solving some real [i.e. broadband] problems where Zo is not real, not
even close, and
you'll see how important it is to use the whole danged complex expression.
rho = (Z - R)/(Z + R) is a complex function as are both the driving point
load termination Z and the reference impedance of the transmission line R.
rho is complex! Get over it.
Indialantic By-the-Sea, FL.