Strange, because I know two (BA mainline) Captains who are seconded there.
Well I won't ask you for names, seniority numbers or 5 letter codes but TBH I'm highly sceptical that they are "bog standard" BA mainline crew, but on the basis I could well be wrong and that you should never say never if I have time this PM I'll go through the mainline seniority list
again and see if I can see anyone with an Openskies annotation .. it will take some time..(
but see foot note)
As Airclues has mentioned back in the day there was an extremely acrimonious dispute between the company and BALPA over the manning of Open Skies. BALPA wanted at least some access to pilot seats, along the lines of the secondment agreement with GSS, management were adamant that they didn't want Openskies contaminated ( that's the word they used) by BA pilots. BALPA lost the dispute (long story, still not fully explained) , and BA certainly weren't in a mood for changing their mind and handing out any concessions to the union.
As I mentioned earlier there was at least one retired BA captain there in the early days, some who have left BA may have migrated there since. Maybe some of our current managers/trainers are quietly being seconded there, TBH I don't know, but I have never heard mention of Openskies secondments being offered to mainline crew as part of the annual bid.
zzz: I stand corrected, I've checked with somone in the know and despite all my waffle above it seems it certainly was an option for secondment a handful of years back (e.g. it was being discussed elsehwere in 2010). Whether the two you refer to are legacies from that era or are more recent secondees I do not know.