Wallpaper over spackle

Of course you can. Future owners of the house will swear at you to no end, but that's their problem, right? ;)

You will need to take off all the glue if you want a good finish.

The paint will lift the glue, but unevenly, and mix with the paint. This will cause the paint to clump and not cover properly and all in all it will look terrible.

I know because I did this in the first house I owned and had to wash the walls of the one room where I tried this several times to get as much glue off as possible. I don't think I got it completely off and you could still tell.

If you just want to paint the room, you would be better off hanging lining paper and then painting that. This has the added advantage (especially if you use 1000gsm paper) of covering any imperfections in the wall.