Can you.... Yes

Should you.... NO!!

The GPU will work with the PCI power from 1 PSU and the riser power from another, but the issues arise if one of the PSU's fails or turns off... If one PSU dies or is on a different circuit and the breaker trips, your GPU will receive only partial power from either the PCI or riser, which will mean it won't work properly and can lead to issues like overheating, shorting out, etc.

The best advice would be to ALWAYS connect a GPU to the SAME PSU. With this setup, if one PSU goes down, the GPU's connected to that PSU go offline too, but it won't harm them.