Yes, a Cab1 can be used with a Base3 using the Base1 > SER2 > Base3 serial connection. It was very responsive in testing.
And to confirm what was discussed above, the Base3 does not share electronics with the Base-1L. The Base3 is a ground-up design, with the main processor generating the tracklink signal for TMCC/Legacy. The only shared component is the radio that interfaces with the Cab-1L/Cab2 remotes.