See? This Set has many Superman figures in it.

A miniature in a miniature set that's miniature to the miniature,.. Minaturception

Can these be played without using toyman?

Yes. They are similar to Flocks of Bats or Lockheed in that they can be played attached to a figure (or team base in Lockheed's case) or as separate characters similar to 3-D bystanders.

I think wiskidz use the same sculpt as the common superman from the DC 75 set

Do these and the flocks of bats break theme or are they like the bystanders where they don't affect theme at all?

It's been ruled that they break theme.

True, these figs usually break theme; however, note the trait:

"When you build your force, Superman Action Figure has all keywords possessed by a friendly character named Toyman"

Kind of sad how a Superman Action figure sculpt is more detailed than most "real life" Superman sculpts.

How I wish these toys couldn't be targeted by EE or pulse wave.

I would like to make a team with four of these and gizmo to give them all superstrength or ranged combat expert.

I had great fun with 3 of these little guys on a theme team with Toyman, fast force Mirror Master a few other toys and an Orange Power Battery. The pocket Supermen made a mess of things against a GotG team with Major Victory, Starhawk, and Talon. The mental image of a 6 inch Superman flying around cutting people's Achilles tendons with a pair of scissors larger than itself was enough to make both myself and my opponent laugh. Then I gave him a Boxing Glove!

what's stopping me from using this to activate eradicator's reign of superman trait?

This figure is called "Superman Action Figure," Eradicators trait only occurs when a character named "Superman" dies.