DDAC is an effective and safer way to treat tarmac rather than using hypo. That's after the tarmac has been power brushed/power washed to remove the bulk of the moss, grime etc.
I'm always wary of letting strong hypo get on to tarmac. That's because I've seen pics of bleached tarmac staining posted on various forums. Still when doing the likes of render cleans etc using a weaker hypo mix 1-2 % from my own experience has very little bleaching effect if at all. Probably because I soak down the tarmac first, don't let the run off sit on it too long and is rinsed down thoroughly.