I bought an eMotimo cart for use with my TB3, will it work with spectrum?

Yes, you will a new motor cord that uses the new locking ports on the spectrum.  Grab the 19" one from the eMotimo store.  

Physically, you will need to get the base of the spectrum over the top of the cart to allow for full pan rotation.  A small ball head or monopod head will do it easily.   We might make a simple riser that is just the right height if there's enough interest.