Can the Ruler Trick be used for chisels? Yes. Should it be used for chisels? Depends.
Yes, the RT affords an advantage similar as with plane blades in honing the flat side of the blade. The tiny 1/2° bevel created by the lift of the ruler makes it faster and easier for your finest grit stone to contact the metal on the flat side all the way out to the apex of the cutting edge. This makes resharpening easier. It also makes preparing a new chisel easier unless it fortunately has a minute hollow on the back to begin with. For example, I recently bought this DeWalt chisel (below) and set it up as a scraper chisel. Remarkably, it came with a nice slightly dished back.
However, that 1/2° bevel on the back of a chisel has consequences in use. For paring, there is a less definite feedback to sense the angle at which the chisel will bite. We want to sense the lowest angle at which the chisel cuts wood. The long handle and a full flat back of the chisel aid that sense. A tiny bevel on the flat side confuses it a bit.
Now, this is in my hands. You may find you can adjust and recalibrate your feel so you can pare just as effectively.
For chopping, we often want to sense vertical, such as in dovetail work. The tiny RT bevel makes that sense slightly less definite. Again, you may find you can compensate and it is no problem at all. As with almost everything else in woodworking, there is more than one good way to do things but it is important to be aware of what is really happening at any cutting edge.
All of this applies to Western style chisels. Japanese chisels do not need the Ruler Trick. The hollow on the back of the blade minimizes the area that contacts the stone and thus the amount of metal you have to remove to hone all the way out to the cutting edge. This is a huge advantage of Japanese chisels, and one of several reasons I use this style of chisel almost exclusively.
Next: There seems to be different opinions on the direction to apply the Ruler Trick honing – across or along the length of the edge.
