I just wonder how Scouts can have "any" cultural exchange because they are in fact scouts because they dont have "soaked" up all the culture of their chapters yet (and lack of expirience) - and without the status as battle brother they wont see the true chapter culture. And in my interpretation of the fluff I cant see any reason for scouts beeing some beacon of "unity". They are trainies, their chapters are responsible for their actions but by no means an ordinary scout can have any official representative function for his chapter, he is in fact no battle brother by the codex astartes. And espcialy chapters like the Dark Angels, Ultramarines or Black Templars wont let go any Scout from their real chapter training. The Dark Angels would be afraid of some wrong thoughts in the Minds of the Scouts, the Ultramarines would fear the influence of a furiuous Space Wulf that could erode the disciplin while the Black Templars have their own special Scout-"programm". I think no Chapter would send a very good scout (And for such a "unity"-event it has to be a worthy one) to send him of the "chains" of the champter. These are the battle brothers of the vuture, the only thing they have to know is about the chapter and their enemys. The Black Templars dont need their "Scouts" educated by the "arrogant" Ultramarines. Well, thats my view on the fluff but in the end its up to the gm.
I just wonder who played the the sergeant of the squad, atleast there has to be some kind of veteran, mostly a vet-sergeant because even if this was a project of unity there has to be a sergeant. And the "training" as you say is the deployment. No scout is only exercising his training lessions, in fact scouts are a regular force deployed by space marines because only real battles can prepare for real battles.
And for their status. Yes, they are no full battle brothers… but how would you feel in a grimdark theocracy when you meet a soldier (depending on the status of his implants taller/stronger/etc. than you) that is chosen to become the incarnation of the god-emperors wrath, to become the bringer of doom, an angel of death, a holy warrior? Who cares if thats an angel of death in training? ****, this man is what the legends are made of. This man stands for all hope than mankind can have in the most dire situations! If an imperial citzen is in his darkes hour, he will pray to the emperor to send his angels. No matter what rank they are made of. That is more authority than the most cleric players will ever get. For an imperial citizen there is no difference between a scout and a battle brother. All he has been tough of the space marines is their status as demi-gods, angels or what ever they call them on their planets. They are the emperors finest. And to be chosen to become one of the finest or die, is more than any rightous citizen can even imagine.
If you attach such an individual to a regular akolythe cell other players will be outclassed. Yes, such powerfull individuals like Inquisitors might have some power about a lone scout. Okay. But do you realy believe a sector gouvernor has the guts to imprision a scout? He might be no battle brother but atleast he is an astartes and therefore untouchable for any authority beside the high senate, the chapter or the inquisition. Yes, he still might get shot in a dark croner of a street but in any official or non-combat situation he is a friggin astartes acting in the name of the emperor, more than the most others will ever do.