BuddyPress.org

sure but you will need to modify a few theme files and wrap the post forms with a check

theme files contain the “Post a New Topic:” forms
groups/single/forum.php
forums/index.php

then some check like so
`if ( !bp_is_group() || ( bp_is_group() && ( is_site_admin() || groups_is_user_admin( bp_loggedin_user_id(), bp_get_group_id() ) || groups_is_user_mod( bp_loggedin_user_id(), bp_get_group_id() ) ) ) )`