what do you mean "is he for real"?
the reds have ruben mateo, wily mo pena and reggie taylor sitting on the bench right now, not to mention jacob cruz, emil brown, robin jennings and russell branyan in the minors.
mateo and pena are both out of options, so it will be hard for the reds to let go of them *and* hard to justify them both sitting every day.
guillen is obviously a talented hitter making the best of his opportunity while junior is out. at best, you'll get two months of 280 average with 12HR 20RBI. the more likely possibility is that he cools down and one of the many others will be given a shot to get hot.
bottom line--if you need two weeks of help, do it. if you're looking for a longer term solution, faggedaboudit.