The bear wasn't immune to fire, it just took a long time to kill him due to his size. If he HAD been a White Walker, he'd have shattered into ice shards when he was stabbed with dragonglass.
No, Viserion is not a White Walker until stated otherwise - apparently you can only make a White Walker from a still-living thing (i.e. a baby).
....wights are highly susceptible to fire. That may make it difficult to reconcile with him being a wight. One blast of fire from another dragon could kill it.
I don't think the TV writers thought that through very clearly, though...indeed, it seems possible that NONE of the dragons will be killed by the White Walkers like this in the books (i.e. that Viserion gets controlled by Euron Greyjoy using a dragon-horn).
Dear god...I wouldn't put it past them if the showrunners state "it's a wight-dragon", but ignore that it should be vulnerable to fire.
But I wait to see what the HBO website says....
Debate wouldn't be productive. We have only one week until we get more info to go on.
I think there's more evidence of "wight-dragon", here, rather than "dragon-white-walker". Re-animated from the dead seems the determinant.
But there's room for some uniqueness in a wight-dragon. There's magic in a dragon, not found in an ordinary horse or bear. Dragons are fire, made flesh. Wight-dragons don't have to be vulnerable to fire in the same way as wight-horses, wight-bears and wight-humans.
I also think that HBO is going to leave us hanging, here, until Season 8.
Yeah, it might simply be a case - even in the TV show - of "well, they cast a unique magic spell so the wight-dragon isn't vulnerable to fire". Fair enough. I only get annoyed when they just plain forget.
The Viserion we saw at the end of S7E7 had damaged wings from his death fall, or the ice spear. That makes a solid case for wight-dragon, rather than white-walker-dragon.
Like any other wight, he can be damaged to dysfunction by conventional weapons, or destroyed by dragonglass. Still an open question as to whether wight-Viserion might be vulnerable to dragonfire, from a living dragon.
Personally, I would deploy a flight of two Dothraki Longbow Dragonfire Gunships. Rhaegal could carry two Dothraki archers, as well as a pilot. Drogon, four archers, and maybe even a small ballista. All armed with dragonglass-tipped rounds.
Well if you look closely at Viserion's eyes they resemble a white walker much more than a wight. A white walker and Viserion's eyes are clear blue with a pupil, whereas a wight's eyes are cloudy blue with no pupil. Also there is the fact that wights are created diferently to white walkers. As we saw Craster's baby and Viserion were touched by the Night King whereas the wights were simply raised and finally both white walkers and Viserion are immune to fire and not the wights. I dont think the show writers did all of this for no reason and were just bad writers.