Here is small snippet of code to check community level role in Themes. You can write the following code in init_custom.vm

#* Check for Community role for logged in user. *#
#set ($blogEditorCummunityRole = 'Blog Editor')
#set ($userHasBlogEditorRole = 'false')
#* Get Role Local Service *#
#set ($roleLocalService = $serviceLocator.findService("com.liferay.portal.service.RoleLocalService"))
#* Get All community Level Role for current community and Current Logged In User *#
#set ($communityRolesforUser = $roleLocalService.getUserGroupRoles($user_id,$group_id))
#* Iterate through the list of roles and Compare the Blog Editor Role *#
#foreach ($communityRoleforUser in $communityRolesforUser)
         #if ($communityRoleforUser.getName() == $blogEditorCummunityRole)
               #set ($userHasBlogEditorRole= 'true')
          #end
#end