Dean:

I have scarfed 3mm Okoume ply a number of times without structural problems. I use the 12:1 tapered scarf and epoxy. It can be a little tricky cutting the scarf because the ply is thin so the following might be helpful:

Cut the scarfs on a hard, dead flat support underneath. I use my table saw top.

I use a piece of sandpaper glued to a board to make the final "cuts" to avoid damaging the very thin edge. This is really only a concern if you intend to finish the scarf areas with a clear finish such as varnish and you want them to look nice.

Make sure the two pieces are scarfed identically in width and that you have taken the wood down evenly. I check the "flat" of the scarfs with a straight edge. Use the lines created by the plys to gauge how even your cuts are. The edge at the end needs to be "sharp". This takes practice and the occassion "redo" to be sure it is right. So don't cut your panels to length until you scarfs are made.

Structurally, I've never had a problem with a 3mm scarf.

Craig