If the Walkera heli has a Spektrum DSM2 or DSMX compatible receiver, then yes, you can use your DX6i. If not, you'll need a Spektrum DSM2 or DSMX compatible receiver.
Which Walkera are you planning on getting? If its a micro, then the RX is part of the flight board and can't be changed. If its a larger one with separate RX, then you can just swap it out for a Spectrum one.