If that's the rule, then I guess not. However, why do we not allow cash after the trade deadline? It doesn't seem fundamentally different than trading picks. Neither involves trading players who can play, which is why you have a trade deadline and makes sense. It seems like you should be able to trade cash like you can picks. The deal probably works anyway, but the cash was mostly to help him sign picks, to help him out.
Is there time to send cash and sign picks on the day the playoffs end, right before the offseason, or do picks have to be signed earlier?