Update: I just dug out an old HDD that came with one of my old macBooks that has Snow Leopard on it. It took awhile but I got it booted with Clover using a number of settings. I was able to boot using my gt210, and the first boot was with nv_disable=1. You may be able to boot and load your SL disk using a clover USB bootloader which will give you many options as opposed to iBoot. I'm writing this from my Pentium G3258 with GT210 in Snow Leopard with my High Sierra SSD as my boot drive. It has the latest clover in UEFI mode so it is possible to boot into SL with Clover.
I used clover settings.
Boot arg. dart=0 cpus=1
ACPI drop tables= Drop ALL OEM
CPU tuning = halt enabler, pstates, Cstates C2, C4
Graphics = Inject Nvidia
Binaries = CPU Fake ID 0x106E0, kernel pm, appleintelpm, AppleRT, DellSymbios
I have wifi (TPlink N900 Atheros 9380), Graphics have support GT210.
View attachment 306250
Maybe if you use boot arg. PCIRootUID=0 and nv_disable=1 you may get past graphics error.
I will try with my RX 460 to reboot using these settings and update this post.