the way i understood it was that yes you can't sign and trade players that weren't on the roster on the end of this season. They would include green, nenad and wilcox.
Last year Orlando got baby davis and von wafer on sign and trade deals in the same deal i think, think they added the wafer deal cos of the base year compensation rules, that is if you trade a player that receives a 20% pay raise over the previous year, the higher of half their current salary or the previous year salary gets counted as the outgoing salary.
So if they traded away bass and he got 6 mill, then only 4.25 mill will count for salary matching purposes as outgoing salary, but the six million will count as incoming salary for the signing team.