This should be compatible. Both I/O voltages are 3.3V
Connect Rx->Tx and Tx->Rx
and connect a ground pin GND->GND
On the Explorer you can use D0 and D1 as Rx/Tx, these are connected to Serial
On the Explorer in Arduino Code:
Serial.write / print / println
On the Pi you don't need to do this in Arduino Code.
Let me know if you get it to work.