I used to work for a company that teaches people how to take the GRE and other similar tests.
What Snarky_Kong said is a large part of it. The words aren’t generaly terribly obscure, but yes, knowledge of roots and etymologies and so on will definitely help on the GRE, and it’s designed that way.
Back when I taught the GRE, my company did have flashcards students could buy, but they worn’t just straight word/definition flashcards. Rather each card contained a list of words that are semantically related. You weren’t supposed to memorize definitions, but rather, find ways to remember that this list of seven words are the “cat” words (i.e., words that mean roughly something having to do with the concept of cat.) (There was no actual “cat” group I’m just having trouble remembering an actual group.) This kind of very vague, rough, impressionistic knowledge of vocabulary often suffices. (When I read about this in training I thought it strange, but since then came to realize that actually, my own knowledge is organized in this way somewhat and actually does help me when I take tests like the GRE. I’d just never noticed before.)
It also helps to have even just the vaguest knowledge of connotations even if you’re not clear on exact definitions. Knowing a word has negative connotations, or connotations of murkiness, or whatever, can help on many of the GRE question types, like sentence completion. (It is a multiple choice test.)
The GRE is designed not to test a bunch of individual bits of knowledge but rather the ability to use one’s knowledge to answer questions about things which one may have no immediate familiarity with. So, for example, in the math section they’ll throw you a problem containing a whole lot of greek symbols and trig functions and whatnot, and you might panic–but the trick is, all the weird stuff cancels out and the expression really turns out just to refer to 1, or to 3x, or whatever. So while you may not be immediately familiar with the value of the greek-lettered constant, or the means of calculating the trig function involved, still, you can solve the problem if you have reasonable knowledge and understanding just of how math and numbers work in general. That’s the way the GRE is in the vocab section as well.
IMO if your friends are walking around with flashcards trying to memorize individual definitions of individual words, they are making a mistake. For the GRE, this is unproductive–indeed, I’m tempted to say it’s counterproductive because it wastes a lot of time.
-FrL-