Can I float a tongue-and-grooved 1x12 pine floor over a concrete slab on grade?
You can float wood flooring installs over concrete. Moisture is your primary enemy here, and uneven concrete will also be evident in the finished result.

I would consider painting on a moisture barrier, and then using a moisture/sound/mold/mildew/pad atop that.

You should absolutely glue the joints. Set the first three courses straight and true and let the glue dry overnight. Afterwards, glue each joint and use blue painter's tape every few courses to hold them together. 

An uneven floor will show up more if your wood isn't beveled, and you'll notice dips with "springiness" in the finished wood floor.