1, If you measure a simple resistor with an ohmmeter you will see its impedance, which has no reactance. Everything is impedance measure. When you measure source/drain impedance you should see the resistive part of the impedance, so basically it is resistance, but reactances always have some negligible effects, and you should never forget what you see is still impedance.
2, AC, small signal
3, independent sources not physically shorted or opened, just in the small signal equivalent model. These are used to simplify AC calculations like gain, but not real or viable models. Under real measuring test signal has to be AC coupled, which doesn't modify the operation region of the device.