If my state of residence is CA, my spouse's state of residence is TX, but we are stationed in OK do they have to pay OK tax or are they considered a TX resident w/MSRRA?

Yes. Your spouse will have to pay Oklahoma tax unless they have the same residency as you.

Oklahoma says:

When the spouse of a military member is a civilian and has the same legal residency as the military member, the spouse may retain such legal residency. They file a joint resident tax return in the military members’ State of Legal Residency (if required) and are taxed jointly under nonresident rules as they move from state to state.

If the non-military spouse does not have the same legal residency as the military member, the same residency rules apply as would apply to any other civilian. The spouse would then comply with all residency rules where living.

See page 3 of 2021 Oklahoma Resident Individual Income Tax Forms and Instructions