Advantages of using a current loop in driving a BLDC motor
Yes, you can just drive BLDC motor only with velocity loop.
But please note that without current loop you can overload current of stator coils when torque  and power at the shaft will be higher than rated. 
Secondly, if you control current - it's possible to control torque directly. 
When the load on the shaft is being increased - it's faster to detect increasing current than decrease of velocity of motor so response time of regulation control is faster.