I rehydrate in water with a little GO-FERM. Can you use wort? Sure. You can also use more packets of yeast if you are concerned about viability. I guess the rehydrating thing with dry yeast is still way less hassle than what you'd do to make a starter for liquid yeast that I think it isn't a big deal. It only takes 15 minutes. If it helps the yeast acclimatize faster and get going quicker, it's worth it.
As with most brewing choices, it's not a yes it will work/no it won't question. You're dealing with probabilities. Chances are it will work. Chances are better if you rehydrate properly. Is the difference significant? Really hard to tell except after the fact. In my way of thinking, I'll always go the "cheap insurance" route if it isn't a lot of extra work. If I get an inferior batch and then tie it to not taking an extra 15 minutes (of which only about 30 seconds are actual work), then I'd feel like a putz.