What you’re describing should work fine, just verify the TTL output with a meter per the instructions and you’ll be fine. Sounds like you know what you’re doing:) If the laser driver has it’s own power supply and isn’t sharing a power supply with the RAMPS board then you don’t need to worry about soldering a resistor across the TTL outputs.
ONE LAST THING: I noticed that the older “WALYE A-8 and A-10” drivers weren’t sensitive to polarity on the power supply connection and would work connected either way but the newer “Good laser” and other variants are sensitive to polarity at the power input. Just be careful and verify everything as you go. As you can see in the attached pics, The properly seated JST power connector has the positive lead closest to the edge of the board but when I flip the board over I see that it’s actually the negative side that should be closest to the edge. Not sure if the JST-XH connector is soldered to the driver upside down or if my JST-XH leads are backwards. The marking on the driver board is correct though, it’s actually the negative side that’s at the edge. Just be aware that stuff like this happens with Chinese QC inspection from time to time. Don’t assume that your red connector leads are actually connected to positive terminals, verify against the markings on the driver PC board.