Nierrese support or condemnation for the rebels would entirely depend upon what Nierr would get out of either, allowing or disallowing the rebels access to organisations Nierr would be the result of that
For example (and I've not been following your rp, apologies) I would either - were Neirr a member of the DU and if the DU had passed resolutions to set out such - allow the Rebels to join as some kind of observer/junior member or make it clear to them that the DU expects the rebels to abide by established limits upon warfare, especially with regards to civilians, child soldiers, mines, etc etc.