Re: Seeking advice on a frog and plant rack build
I have been puttering around with woodworking for the past 15 years. To be clear when I am talking about a veneer it is a thin piece of hardwood glued over some lesser wood or engineered wood product. Is that what you mean? If so that is not really an option for you on raw 2x4s. The rounded over edge of a 2x4 means you cannot glue a flat piece of veneer to them and have it look not terrible.
If you are talking about skinning the shelf so you put large pieces of ply or hardwood or whatever covering your joints then that is fine and not uncommon.
If you are asking which to do, then I would say that with low quality pine and engineered wood you should consider paint as it will hide the grain and make the use of engineered wood less obvious. An outdoor rated paint would be my choice for anything that might have water exposure.