My goal is to reset RPi Zero by another MCU when I need to. Say ESP8266.
This is my 50cents:
H5 is connected to a RUN header of the RPi. When HIGH, it is OFF. When LOW it is ON.
Is this ok approach or should I do a change or two? Did I miss something?
Plausible. 
No, potentially this cannot work:
Is there a load resistor (pull-up) after Q8 (on collector side, pin 1 of H5)?
If you try to close transistor Q8 - it will not find any load. Let's assume H5 is the header with the reset pin of the RPi Zero: in case there is not any pull-up - the Q8 does not have anything to work against (the reset pin of RPi Zero remains floating).
There should be a pull-up on H5, pin 1 (at least on RPi Zero board).
BTW:
When both are 3V3 logic: you can wire the GPIO15 directly as input for the reset. A high vs. low would reset the RPI Zero. Just make sure you have GND wired between both boards.
Potentially you do not need Q8 (the GPIO15 can still drive in the same way).
And: with Q8 you invert the logic: now GPIO15 has to be high in order to let switch Q8, generating a low (for the reset).
"RUN" is pulled up to 3V3.
rpi-zero-v1_3_reduced.opj (raspberrypi.com)
This makes sense.
But you can use still a direct GPIO15 pin to control (no need for Q8).
Never mind if "totem pole" ("push/pull" = PP) or even "Open Drain" output on GPIO15 - it should work (if all is 3V3).
Strictly speaking, it does not matter about the voltage. Just use a diode with the cathode to the controlling I/O pin and anode to the Zero. A Schottky might be best.
The specific advantage of the transistor is isolation - if the controlling device is not powered, then the Zero cannot be reset. With the direct connection, powering the controlling device off will tend to hold the Zero in reset, probably not desirable. The implicit logic conversion is highly desirable.
Oh, it most certainly will. 
Even not knowing the internal design of the Zero offhand, I know it must include a pull-up resistor on the reset line. It is simply not negotiable; it could not possibly work otherwise. 
(And the pull-up may be internal to the microcontroller.)
But if it has already pull-up as it is mention above?
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