f I recall correctly, the full installer for ZEVO 1.1 (released 2012-09-15) should remove what was installed by the (then) installer for stable MacZFS.
Whether greater care is required with the newer approaches to non-stable versions of MacZFS, I don't know.
Cross reference:
(This topic focused solely on the full installer and update for ZEVO Community Edition, both of which are provided by GreenBytes.)