Cement board as paver base?
While they do make exterior cement board your issue is really going to be that of loading and exposure to other elements. 


You will have pavers and then a person standing on them you may exceed the loading (although they are used as a base material for underlayment of ceramic floors there is additional support across the board - your ground may not provide that support. 
Further you will also have the elements at play here chemical composition of various components of the soil and rain water (is your rain water alkaline in nature or acidic) and what other contaminants will be in it as it washes the board over time.
You will have issues with shear over time as people walking on the top of the pavers, ground movements from vibration of nearby roads, perhaps trucks or trains - also your ground might be subject to subduction. 


Please look to the following for more information:


See page 141:
https://www.usg.com/content/dam/USG_Marketing_Communications/canada/product_promotional_materials/finished_assets/cgc-construction-handbook-ch04-cement-board-construction-can-en.pdf
See Page 2 and up: 
http://www.usg.com/content/dam/USG_Marketing_Communications/united_states/product_promotional_materials/finished_assets/durock-cement-board-system-guide-en-SA932.pdf