With vinyl tile, whatever the condition of the floor is under the tile is what you'll get in the tile. If there is a bump or pit in the subfloor, you'll get a bump or pit in the tile. Floor paint will do the same thing, but even more. If you are OK with that then a scraper to get off the big, loose chunks will do. Otherwise I would install a self leveling floor base or grind off the glue with a concrete floor grinder, followed by filling in the pits and cracks with an appropiate filler.