All your friendly units will get their bonuses for rankup. However, that skill activates only once on a card, so for example:
gowen lvl5, highland hunter on the field, 50 HP, Rougeerst SS activates: highland huter already has his rankup, so he only gets +2 lvl, +20 AT, and the healing.
Its the same way around, if you rank up your unit with the SS, it wont get any bonus if you increase your gowen lvl to the needed amount. However, of course once the unit dies, it loses the buff of the SS, so you'll need the sphere later on.