Summers was a Hamer endorser early on, they even built a signature model for him in the early eighties which was first called the "Prototype" and then some other name that never stuck in my memory.
Sting was always willing to try new things as a bassist, disenchanted with Police's limitations as a trio (don't tell ME how he did his best music in that format, TELL HIM!!!), he was always looking for new colors: From fretted to fretless, from passive to active, from bass guitar to electric double-bass, I don't doubt for a minute that he would have tried an eight-string fretless in the studio or live as well - eight-string AND fretless, even I haven't come up with that combination yet! I assume that Hamer used some of their know-how from Tom Petersson's eight-strings in the process.