I have a bb with a different carrier, if I install the Verizon OS will I still be able to use the GPS function fully?

I believe so. I think the GPS is just crippled/disabled/"whatever Verizon wants to call it" on the Verizon devices.

I will say yes, you can use GPS on non-VZW 8830 with VZW OS. I have VZW OS on my Sprint 8830 and the GPS works just fine

Correct. Changing OS's doesn't enable or diable GPS. GPS is disabled based on vendor code of the device. It's not anything we can change.