V2.2 is pretty old by now. As far as I recall it should work fine.
V2.2 of the arduino eclipse plugin should work fine with the arduino IDE version 1.5.8. What that phrase wants to say is: the plugin V2.2 was released before arduino IDE 1.5.8 was released; as such the code can not make a statement on the compatibility.
But again V2.2 is old. We hope to release V3.0 end of februari 2016