Dual Power Supply for single 10m LED Strip Run
Are my scenarios safe? / Would they work?

No the first one is  not safe
Yes the could work under ideal conditions, if the supplies were balanced  and the strip were balanced and the cables were balanced then this could work. This balancing is probably not possible in real world conditions.
What is more likely to happen is this:
Any difference in voltage will manafest itself as large currents, lets say the led strip was 1Ω across the strip, an 0.1V difference would generate 1Ω/0.1V = 100mA of current that would be wasted as heat in the cable. Many supplies are not matched and are less than 0.1V (especially cheap ones). An 0.5 difference could be 500mA and so on. The current could be so large it could burn out a cable or the traces on the LED strip.
Case 2 is probably OK, but you will also need to ground both supplies together, otherwise the digital of the 2nd supply will have no reference and no way for the return current to get back to the NodeMCU.
You may also want to consider a buffer IC to digitally buffer the digital from the NodeMCU, check the fanout on the LED strips. If they pull too much current on the digital pins than the NodeMCU GPIO's can source then you will need a buffer.