I'm not sure about this, but I always had the impression that nyanchan translated episodes of AnS (e.g. this one (http://nyanchan.livejournal.com/32995.html)) but did not actually do subtitling. If ever she posted links of shows with her translations, the subtitling work were done by other people like techni_teddy and yuckie_chan. So I think it would be better to ask permission from them as well.

However, it would still be good to ask nyanchan if her translations can be used for subbing even if other people have already done so. It may entail a little more legwork like looking for the raw files, but at least the translation is already there.