They will if you throw them as the grenade charge. In my case I consume the grenade like you would as a Voidwalker. It gives me five. I can summon about 30+ threadlings give or take in about 10 seconds. When I want big damage I consume my grenade, cast my rift which summons 10, cast my super and that refills my abilities. I consume my grenade again and pop my rift for even more threadlings. It’s mad.