Binding UM carrier to jury verdict

Does putting a UM carrier on notice of lawsuit bind them to a verdict in excess of liability coverage, or do you need to join them in the suit against the tortfeasor?

You don't have to join them. Just put them on notice. See: Keel v. M FA, 1976 OK 86, 553 P.2d 153 "ΒΆ28 With this decision an insured who has a claim against an uninsured motorist has the following options:
(1) He may file an action directly against his insurance company without joining the uninsured motorist as a party defendant and litigate all of the issues of liability and damages in that one action. Associated Indemnity Corp. v. Cannon, 536 P.2d 920 (Okl. 1975).
(2) He may file an action joining both the uninsured motorist and the insurance company as party defendants and litigate all issues of liability and damages in one action.
(3) He may file an action against the uninsured motorist without joining the insurance company as a party defendant, but give adequate notice of the filing and pendency of such action to the insurance company so they take whatever action they desire, including intervention."