Any amp with a F/X, line-out or slave-out jack will drive a slave amp
You could connect your Fender in the normal manner and run a cord
from the slave out (or FX/line out) to the FX return of the Ampeg.
(this will make your Ampeg sound more like your Fender)
You could reverse this scenario and output the Ampeg to the Fenders
FX return. (If it has one)
In either configuration you can also use the second amps normal input,
but this ends up giving you less control over your second amps sound
because your stacking two preamp/EQs signals at the second amp.
You could also run both simultaneously, (and retain the tone of each)
by running from your bass to the input of an A/B/Y box. Then connect
one output to your Ampeg, and the other to your Fender.
This method would give you foot switchable control over using either
amp separately or both together.
Note:
On my Mesa 400+, the slave out jack is a attenuated signal from the
speaker output section of the amp, and my FX send jack is a preamp only signal.
I'm not sure what your Fenders slave out signal actually is, but I'd assume its
just a basic (preamp only) line-out jack.
But if your amp has both, you might prefer the sound of one over the other.