I've seen the slow-mo video a few times. This one can be debunked very easily tbh and people are looking too much into it. It's a developer thing. They basically removed Albert's character model (at least his head) from the game when the rockets blew up. The reason for this is to have the explosions look better. Otherwise we'd see an object inside of the explosion and it would look like crap. Capcom just removed him for technical reasons. I believe in the full video his entire body was removed. First his head, then the Uroboros part. It's possible that they were two separate objects.
So no he didn't teleport. They literally highlighted his character model (head) and hit delete on the keyboard and replaced it with the rockets exploding. Rocket's don't even explode in a video game. When they come in contact with another object with a collider (proper term for a solid object) an explosion animation is played over it and the rocket is moved destroyed and removed from cache. So they look like they physically explode, when really. They don't.
Albert's head likely has a separate box collider on it, because it would be easier to program so headshots would deal more damage than body shots when you fight him. Oh... and Albert can only teleport in short bursts. He would have needed to go a very long distance.
I think the guy in the wheelchair looks more like the old man in the pictures and here.
I think he's either a new character. Or a flash back or hallucination of Spencer to capacity. The latter seems to be a popular theory floating around, but it's very likely the be the former. Some have suggested that it's a woman in the wheelchair, but I don't think so.
That's very interesting. Though I suggest Paul Birches comment. He pretty much nailed it. Since a lot of the cooperation's in Umbrella Corps are jokes and references to other games like Street Fighter. I honestly think that it might be related to Shéng-Yā Pharmaceutical. They were recently introduced and they are rumored to be the same rival company from RE2. The one that Ada is presumably really working for. Shéng-Yā Pharmaceutical also has some connection with Alex Wesker. As they are still developing her character. Both of these things are in Heavenly Island and it takes place in 2014 I believe. Albert could be back, but as far as we can really say. Alex Wesker is the only Wesker now.
On a separate thought. Why do people claim "The Experiment" is hard? I haven't beaten it yet, but I think I'm getting close. So far it seems really easy. The crows are a bitch.... but I'm not having much difficulties and I got S ranks on all the challenge missions so far.