Have you tried Xsim? It is a crossover simulator, but you can place different drivers in series and get combined frequency response and impedance. You need to have .frd and .zma files for the drivers, but even if you do not have these for your own drivers you can use other drivers to get an idea of the effects. Dayton has that info for nearly all of their own drivers.

The impedance curves of different drivers in series will interact to change the frequency response of each. The greater the mismatch in the impedance curves the larger the effect will be.

Line arrays are a special case, since the drivers in a line will be of the same model. Ideally they would be identical in all respects, but manufacturing tolerances make this unrealistic. Over most of the frequency range this variance might typically amount to just a fraction of a decibel difference. But if the drivers have a wide variance in Fs this has the potential for a bigger problem. Suppose most of the drivers have an Fs of 50 Hz, but one in the line is at 40 Hz. That driver will produce a greater share of the output at 40Hz, and would reach its excursion limit before the others in the line. Connecting multiple drivers together in series-parallel (such as the 3-by-3 arrangement mentioned above) can help mitigate this by averaging the impedances together in the parallel groups. Also, a resistor in parallel with each group will lower the impedance peak, though it will also lower the overall impedance and waste some power. I might use such a resistor if I had just a few drivers (the woofer/subwoofer section) on an open baffle and I need to ensure equal excursion near Fs.