Well a backlink is essentially a "vote" to your site from the site that the link is coming from.
If Google doesn't know about that vote (backlink) it cannot give you credit for it.
Therefore, for this reason, all backlinks should be well indexed by Google.
But its of my personal opinion that if your backlink isn't being indexed by Google, then there's a reason for that.
If it's not being indexed, it's probably because Google hasn't crawled that page / link yet.
Then it also needs time to add that page/link to its actual index.
Good quality links on good quality sites/pages are crawled and indexed virtually straight away.
If a backlink takes more than 3 days to get indexed, the source of the backlink is probably not worth having!
That's how I see it anyway.
