If C1 is the first video GNCA-0019, live video with Kawada Mami, then it probably should be deleted, since there's no animation in it at all. Only animated clip on this disc would be second video - "Hishoku no Sora (SHANA version), but it also exists on SnS DVDs and already exists in base as C5.
I think the policy towards this is like this:
If the content in question was included in a officially distributed or broadcast product (just like some commentary or "making of" on a dvd or some teaser/commercial which aired before the show started), then it is allowed to stay in anidb.
Yes, I know. Unfortunately I only have "Hisshoku no Sora" (GNCA-0019) DVD, not "Shakugan no SHANA" DVDs, so I can't tell if same video is included here too.