42 C.F.R. § 137.17
May more than one Indian Tribe participate in the same compact and/or funding agreement?
Yes, Indian Tribes may either:
(a) Each sign the same compact and/or funding agreement, provided that each one meets the criteria to participate in self-governance and accepts legal responsibility for all financial and administrative decisions made under the compact or funding agreement, or
(b) Authorize another Indian Tribe to participate in self-governance on their behalf.