Without knowing the contents of the electrolyte powder you're referring to, this is only an educated guess, but I would say no, they're not the same because their intended uses are different. That drink mix is probably meant to be consumed daily and despite its "electrolyte replacement" label, it won't contain much electrolytes and its main purpose for being in an MRE is probably to encourage drinking by making water (especially chemically treated water) taste better. In contrast, I wouldn't recommend drinking ORS on a daily basis. Too much sodium, for one thing. Try drinking some Pedialyte you get from the drug store some time and see if you would want that with your meals every day. No thank you.

Trusbx already made some good points, and that's a good article he links to. If you ever need to rehydrate someone who is stricken with serious diarrhea or vomiting, while an electrolyte drink may be better than plain water, it would not be the equivalent of a true ORS (oral rehydration solution). They have different concentrations of stuff, and even lack some things. For example, severe vomiting can lead to acidosis. If you've ever mixed up your own ORS, baking soda is usually a main ingredient. This acts to counter the acidosis and bring your pH back in line. On the other hand, your typical electrolyte powder won't help at all for acidosis. That's a good thing, since you wouldn't want to drink baking soda under normal circumstances anyway.

So, if you're concerned about serious rehydration situations, I would recommend that you keep some true ORS handy. You can mix your own inexpensive ORS from household ingredients when you need it. Ceralyte is one brand of prepackaged ORS powder. Bottles of Pedialyte will also work, but are bulky to store.

You might be interested in this old threat on Gatorade packets. If you're interested in some nitty-gritty on how our bodies absorb water, be sure to check out my "physiology of hydration" sub-thread. You'll also find out why I say that electrolyte drink may be better, but may not be, than plain water at rehydrating someone.