Yes, in the sense that the Prophet '08 then takes the Tetra's voice and becomes a twelve-voice Prophet '08. The extra features from the Tetra then won't apply to the P'08.
From the Prophet '08 Manual, pg.33:
Using Poly Chain
Poly Chain links two Prophet '08s or a Prophet '08 and one or two Tetras to increase polyphony by intelligently processing the keys hit and passing MIDI data through to the Poly Chain MIDI out jack.
You should have the same programs loaded into all the poly chained instruments. The easiest way to do that is to use the Dump command in the Global menu to dump the programs via MIDI from one synth to the other.
Note: Tetra ships with the Prophet factory programs already loaded into banks one and two. The Prophet does not have Tetra’s sub-octave generators or feedback, so for poly chaining it’s best to either use Prophet programs or Tetra programs that don’t use those features.
[For a Prophet '08 and a Tetra, connect the former's Poly Chain Out to the latter's MIDI In. In Global, pg. 2, set the Prophet to "Out 4" and the Tetra to "In End".]
You can now virtually ignore the slave unit, since the controls on the master will control the poly chained unit(s) as if they were a single synth. This includes saving a Program; if you save an edited program on the master, it will also save the program on the slave.
Note: If using an external MIDI clock, set the master MIDI clock to MIDI In/Out, and the Slave MIDI clock to MIDI In.
If Poly Chain is set to Off, the Poly Chain MIDI out jack simply duplicates the MIDI out jack.