Remember Mark McGwire? Well, he was taking androstenedione. One of the risks with this prohormone is that is can also convert to estrone.
DHEA actually converts to androstenedione and so you open this same estrogen pathway. Furthermore, the androstenedione will also partially convert to testosterone and the testosterone can aromatize to estradiol, the "bad" estrogen. So the bottom line is that you have two estrogen pathways activated when taking DHEA and so the question is whether or not you get higher T proportionally.
Well, actually, that turns out not to be the question, because DHEA seems to have no significant effect on either T or E according to this study:http://jap.physiology.org/content/87/6/2274.short
"Effect of oral DHEA on serum testosterone and adaptations to resistance training in young men"
For this reason I do not know of many bodybuilders or strength athletes taking DHEA - it just doesn't do much of anything to get excited about.
Now DHEA does have a couple of interesting possibilites, but it has kind of died off in the supplement world due to lackluster results on many fronts...
Bottom line imo is that there are much better supplements for ED.