Short answer is "highly likely NOT" but first I need to correct a misconception found in the replies here.
Nvidia does not "actively disable VM passthrough" (here I'm talking about GTX / RTX cards). The right word is "discourage". What the Nvidia driver does is if it detects being run in a virtualised environment, it will error out with code 43.
Preferring AMD over Nvidia because of error code 43 is like preferring to stand under a coconut tree instead of a durian tree for fearing of having something dropped on your head. AMD cards are not problem free - they are notorious for reset issue.
The bottom line is you shouldn't pick a brand but rather a specific model. There are many users on here who have successfully passed through Nvidia cards and AMD cards so you might want to look around the forum for success stories and use the exact same model.
To reduce the chance of getting error 43 with Nvidia cards, you can follow these 3 tips:
Boot Unraid in legacy mode (i.e. do NOT boot Unraid in UEFI)
Do not use the to-be-passed-through GPU as your primary (i.e. what Unraid boots with) e.g. you can use the onboard as primary or buy a cheapo one to use as primary (assuming your mobo BIOS allows you to pick which slot to boot with e.g. Gigabyte X399 mobo).
Dump your own vbios specific to your actual GPU (see SpaceInvaderOne guide on Youtube for how to do it)
You don't have to follow all 3 right off the bat but chances are if you have error code 43, you will have to end up having to do them anyway.
Now as to why I say "highly likely NOT" for your specific questions
You didn't say what your exact spec is (and whether it supports IOMMU, virtualisation etc.).
OnBoard GPU passthrough varies from hard to impossible. There's no easy way. So at the minimum, you are likely to need a 3rd GPU, even a cheapo one for the audio editing workstation - assuming you want to run 3 VMs simultaneously.
Last but not least, mixing brands is fine. If a card can be passed through in its current slot, it doesn't care what other card is in the other slots on the mobo.