Yes.
1-Fairly prominent in the blockchain.
2-If dealing in USD (which was one of the early claims if I remember rightly) then you'd expect some additional volume on some of the exchanges, particularly since if pirate were to convert all his liabilities to USD and back each week (dealing in USD) he'd easily eclipse the entire MtGox volume.
Neither Gox nor Pirate are the entire economy. Data shows that both fit well within the overall activity.
Daily transactions: uptrend
Daily transactions excluding the highest volume addresses: uptrend
Mt. Gox USD volume: uptrend
Unique addresses: uptrend
Transaction volume: uptrend
At an estimated 200,000BTC transferred per day, 1,400,000BTC per week is sufficient to contain trading and interest payments related to BTCS&T in addition to all other market activity.
How do you know?