I hope (ane believe) their trading wallet and "investor payments" wallet are two (or more) separated wallets! So basicaly - yes, they can wait for other user deposit to pay other user out, while theyre not doing ponzi (because skip the step to send money to trading wallet and in a while withdraw another amount from that wallet)
You wouldnt be implying they are sending out bitcoins that other customers deposited, right? I mean, thats how a ponzi works

.
Or put differently, ask yourself how they can "trade" with no problems, but cant send out bitcoins to investors.
Anyway, its a moot point. bitcoin trader is a glaringly obvious ponzi and it wont take long for everyone to see that. They are just stalling, they will soon come up with other excuses and delays but the money isnt there, it never existed.