Jimmy Seals is not mentioned as playing on any Eddie Cochran recording sessions.   But based on the following excerpt from John Collis' book "Gene Vincent and Eddie Cochran: Rock 'N' Roll Revolutionaries", it appears that the photos of Jimmy and Eddie are of a late 1958 rehearsal for a concert tour of Canada.

"Later in the year (1958) he (Eddie Cochran) headlined on a trip to Canada.....For the Canadian gigs he put together his own band.   Joining Connie 'Guybo' Smith was drummer Gene Riggio from the snappily titled Los Angeles group Dick D'Agostin and the Swingers, with pianist Jim Stivers and, briefly, saxophonist Jimmy Seals.   Seals had played on the Champs' hit of that year, 'Tequila', and would later form a successful duo with Dash Crofts.   As a nod to D'Agostin's group the band was dubbed the Hollywood Swingers, and the departure of Guybo to get married early in 1959, together with Seals, brought in other members of the Swingers including D'Agostin himself."

All of these players are seen in the late 1958 photo session.   However, it is interesting that recording personnel appear to be present as well.   So eventually evidence may appear showing that Seals and Cochran recorded together.