Is it possible to create a sketch or feature and suppress it, and use it as a point to constrain in the assembly.

Yes you can . One suppressed one normal.

Let me explain a bit further. I have two scenarios.

I have three components. A scaffold upright, ledger and steel board. I can constrain the edge of the wedge hole on the ledger to connect to the edge of the v pressing on the upright. But the problem is, when I do that, it isn't in the center. I try and explain in the photos attached.

My other problem is I need to constrain the steel board, to fit onto the ledger at a certain spacing as attached photo.

I have no problems using the normal contraints available.

I used center ,Flush and tangent contraints

You may want to use workplanes and axis for the constraints rather than the features or bodies of the parts. If you go into the part files and create workplanes where you need them, the constrain the workplanes together, the parts will always end up where you want them to be. I do this at my job quite often because not everything we get from vendors is modeled or assembled properly.