These two immediately have a sexual rapport. Ares loves to make love, and Scorpio is a very sexy sign, in that it considers sex to be a melding of spirituality as well as physicality.
The difficulty here is that they're both so strong. Ares is the leader, the one who wants to be in charge, the one who wants to direct the traffic, so to speak. Scorpio will not be controlled. In fact, Scorpio is a control freak. Scorpio needs the stability and the security of knowing that he or she is the one that's setting the rules. So immediately these two are going to come butting heads into the control issue.
I would say that there are good possibilities that they can work this out, but both of them need a lot of patience and a lot of ability to compromise. Therein may also be the problem, because neither one really takes to compromising easily.
What holds them together is that there is a lot of passion, passion for life, passion for each other. But as soon as this cools, they're going to find difficulty in other areas of life.