There are a few ways to view lists of units, the best is probably the military notebook
on our main site. It will not however list what the tech prerequisites are.
You could of course go through the equipment file (SRUNITS.CSV) and tech tree file (TECHTREE.CSV). They are found in the /CUSTOM directory of the game. The two columns labeled "Special" in the equipment spreadsheet have numbers that match up to the "Specific Tech Tree Advances" in the tech tree file. The most current version of the equipment file is also available from our website
There are only a few technologies that don't actually have a design that uses them at all, but you are correct that there may not be a design for a certain tech in a certain region, but researching techs has it's own benefits and they can always be traded for profit.