If my memory serves me correct, Pat Summerall and then-Boston Bruins' TV announcer Don Earle did a short post-game segment from inside the team's dressing room at the end of CBS' coverage of the fourth (and what turned out to be the final game) of the 1970 Stanley Cup Finals (WSBK-38, which was the team's TV flagship then, simulcast the CBS coverage and did a longer post-gamed locker-room segment after CBS' coverage ended). Thuis, I am pretty sure, is the only time he worked an NHL telecast, and only for the postgame segment.
I don't know if this is true, but I once heard an urban legend that Summerall, a CBS technician, and Doug Orr (the father of Boston superstar Bobby Orr) were in the Boston dressing room ready to be joined by Earle for postgame interviews if Boston won the championship. Reportedly, the elder Orr was too nervous to go back to his seat for the start of overtime.
But after Bobby scored the championship-winning goal after just 40 seconds, so the story went, Summerall turned to Doug Orr and yelled over the crowd in the stands above "Mr. Orr, your son has scored and Boston has won the Stanley Cup!". Doug Orr is said to have told Summerall "I know Boston scored, but we didn't see it! What makes you think my son scored?". Summerall supposedly replied "Because they wouldn't be yelling this loudly if (Phil) Esposito (another high-scoring Boston player of the era) had scored!".
I don't know if it's true or not, although I have in recent years seen a clip or two of Don Earle's postgame interviews. But I'm pretty certain Summerall was there for the three or four minutes while CBS was still on the air, with Earle helping out.