I've always worked out, but I've been working out even more heavily the last couple months, no cardio at all - just heavy weights. I've put on about 7lbs since and I'm now more or less as heavy as i've ever been (in terms of lean mass) and my hair is as good as it's been in a while. I am also on the big 3 though.
The testosterone release from working out is VERY short lived... I've actually seen suggestion that those who work out over long time frames end up with slightly lower testosterone.
The benefits of working out, both aesthetically (and lets be honest, your being on this forum means you care about how you look) and in terms of health FAR outweigh the negatives in my opinion. This applies even more so if working out makes you start thinking about what you eat and making better choices. Just stay away from the temptations of steroids or pro-hormones because they DO have the potential to mess with your hair in a big way.