Let me try to make the distinction very clear:
If we ask simply as a matter of definition, "what things are true on Rorty island?", and the answer is: "those things that people agrees upon are true for them", I think there might be a chance of some circularity but I don't really find that all too disagreeable as a working definition.
The central issue is how they figure out what is true on Rorty island or rather, how they ought to find out what is true.
For instance you could say: "They have decided as a matter of practice to hold courts where evidence is brought before the jury and then the jury goes to a room and decide what is true", then I think this is evidentialism in a poor disguise.
If on the other hand you answer that there can be no "how they ought to find out what is true" on Rorty island because this is too much like evidentialism, then whatever practice is held before or during a trial on Rorty island is arbitrary, so is it just as rational (or irrational) to hold proper trials, present evidence which is real (as opposed to fabricated), etc.
I don't think Rorty holds that view but I don't know..