You have to first understand that aliens can be living microcreatures that have to be the green aliens movies make them to be so i would say yes they do

Yes I do think that NASA knows about aliens but are not telling us for our safety/their safety.
The Human race is an aggressive race and if we knew about them some people would want to harm them as humans aren't ready for it, it would be surreal.

the government made MIB to secretly tell us the truth

I believe they are real. The thing about that video is he could be talking about the humans not on Earth, like the ones in space stations. He did put it in a weird context, but I doubt he of all people would leak that information.

If you think about it NASA is just a organization with a big telescope and a few people with above average intelligence. They may know for sure they are real, but so am I, and so are a ton of other people. I didn't watch the video cause I'm in a rush but I'll be sure to when I get time later.