Found the solution, the build of OpenLDAP that comes with IMail doesn't have the same default path as the default path for the install, so you have to explicitly specify the location of slapd.conf eg slapcat -f C:\Imail\OpenLDAP\Bin\slapd.conf -n 1
(if you use the default installation path) (mind you, even after specifying the path, the -d option still seems to do nothing. Oh well, I'll just have to drag the config to my linux box to test it if need be)
