To answer @rcshaggy:
You're right to assume there might be some complicated feelings between the Darkspear and the Zandalari.
They have always been opposites. The Zandalari are the unfallen empire of the Trolls. The "Civilized" Trolls that pioneered civilization, walking upright, and replaced some of their roots and Loa connection of the Shadow Hunter, with the culture of priests and structured rituals of sacrifice to individual Loa instead. The Zandalari are the remnant of the Empire that once stretched all of Azeroth, that was broken by the rise of the Night Elves. They remained at the heart of what it meant to be a Troll in the glory days. And their influence on Troll culture kept their people stuck in the past, wishing for a return to those old days. Feeling that, despite the new races having popped up everywhere, the world was theirs by ancient right. And this guidance has kept the many powerful Troll Tribes hostile, xenophobic and ever-nostalgic for the glorious past.
The Darkspear on the other hand are the outcasts of outcasts. Driven from Stranglethorn, they met up with the orcs, and while never losing their connection to the Loa, through following the guidance of the Shadow Hunters, they adapted their traditions and looked to the future instead of the past. A future in where, with the Horde, they ended up finding like-minded individuals and being a part of one of the two actual-dominant forces on Azeroth. That the Darkspear were on a new path became quite clear when the Prophet Zul led Zandalari forces to rally the Troll Clans to new hostility in patch 4.1, where Vol'jin walked away from the meeting, choosing to stand against them. The Darkspear reject the Troll Empire.
For years now, all we've seen of the Zandalari has been hostile. They rallied the Amani and Gurubashi against us. They aided the Mogu in Pandaria. They were the antagonist in the Vol'jin book as he recovered among the Pandaren, during a dire conflict.
So how do the Darkspear see the Zandalari? Well, a lot is going to depend on King Rastakhan. The Darkspears have been outcasts and rebels. The Zandalari have been rulers and kings. But while the connection to the Loa may be less personal, the Zandalari are still a major factor of troll culture and respect, and they are still very powerful. If Zandalar bows to the Horde, it means he will have to step away from the old ways. Away from the xenophobic pursuit of a Troll-ruled Azeroth. And embrace a new path, with the Horde. Sure, the Prophet Zul was behind most of the recent hostility, and is apparently now leading a rebellion. But it is a huge step for King Rastakhan to move away from the restoration of the Troll Empire. If the Zandalari now favor the Horde, and embrace like-minded non-Trolls and Troll Outcasts as being the path forward. That does a lot to mend bridges.
So in short, the Darkspear will probably view the Zandalari with a mixture of resentment and hope. And how much of each depends largely on how King Rastakhan sells it. He is The Troll King. But in joining the Horde he would have to accept a lesser role as one equal to the other race leaders. The Zandalari and Darkspear may just be about to become equals. If that's how it goes, that would be an epic moment for the Darkspear. If that's cool with Rastakhan, I don't see too many Darkspear hold on their resentment too long.