Basically a resolver produces a sin/cos signal, they require analogue detection circuitry to work, I have some Allen Bradly drives that are resolver only, the encoder signal is extrapolated from this in the drive for output to a controller, this method has been done for some time now for AC sinusoidal commutation, this is opposed to BLDC commutation which typically uses three commutation tracks on the encoder disk, used to be known as Hall effect due to 3 descrete hall effect devices used.
There are current sinusoidal drives that use an initial marker signal and then produce the commutation from the encoder pulses.
BTW, Since Allen Bradley bought out Electro-Craft, their motor and drives have principally been Electro-Craft, often the same part number.
If you replace an encoder on a motor to use as AC or BLDC, the pole count and pole position has to be known or detected and the encoder lined up with the pole position.
Someone mentioned Renco, they have now been taken over by Heidenhain and their product line has been trimmed quite a bit.
Nosmo.