The league has never said that Scott is not eligible to play in the All Star Game. So far the source of that statement is just a TSN "opinionater". As for the trade to another team or even to another conference, that is not a new situation. In the previous instances the elected player participated as a member of the team they were on when they were elected as an All Star. Therefore, the only unprecedented element in this situation is the assignment to the AHL. That action by the new team is easily reversible by simply bringing him back to the NHL level for the duration of the All Star event.
The sad part of this is that a player, through no fault of their own is being put into a position where they stand to be humiliated on a international stage. John Scott worked hard to attain success as a professional hockey player. A 6' 8" , 260 lb enforcer is not likely to fare well in a 3 on 3 format where normal defensive play is not feasible.