Sure, you can use any pair of Vcc / Gnd pins on the OSPi board. Those are designed for connection to external components. You should use Vcc (3.3V) and *not* VIN (5V), because Raspberry Pi’s GPIO pins in theory can only accept 3.3V input.
Note that Adafruit also has a tutorial on interfacing with these temperature / humidity sensors using Raspberry Pi:
http://learn.adafruit.com/dht-humidity-sensing-on-raspberry-pi-with-gdocs-logging/