last i tested successfully was 7.0.7.1 i think.
so unless they made some network protocol changes it should work.
Beware that you need an old client install for 3d character models, the newer uo versions don't have the data needed by iris anymore.
See
http://iris2.de right hand side for links to working installers.
Using the latest installer from official uo website -> no 3d character model data, missing visuals in iris 3d mode, not recommended.
Using and old installer and patching up to the latest version -> 3d character model data needed by iris is still there. That's the recommended option =)