Can't make out what you mean by "isnt compatible with a back plate"... also; a low profile cooler probably won't interfere with the RAM sticks... the ASRsrock FM2a85x itx mobo may have the RAM sockets on top instead of the right, but the socket is also sideways so the socket-to-ram clearance is about the same as in a regular motherboard.
Any CPU Cooler compatible with AM3\AM3+ is compatible with FM2... some are Compatible with AM2\AM2+\AM3\AM3+\FM1\FM2\and Intel 775\1155\1156\1366\2011... Others may say they are compatible with some of these, but they were probably marketed before the latest Sockets were avilable, so obviously they appear to be compatible with 2 or 3 sockets when they should be compatible with all or at least most of them. So, you shouldn't have trouble finding one that's appropriate for your setup. Any that upright should be right for your need.
Check here:
http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&DEPA=0&Order=BESTMATCH&N=100006648&isNodeId=1&Description=am3%2B+cpu+coolers&x=0&y=0