Looking at the Compatibilty Matrix, only 5.0.1 MR1 is compatible with Exchange 2010, would I be correct?
Yes you are correct
Here are some articles for your reference
http://msexchangeteam.com/archive/2009/12/09/453486.aspx
http://na.blackberry.com/eng/support/software/server_compatibility.jsp#tab_tab_overview