The only way to find this is to check out the previous comments where the author has put the links. Then you can view the source of the page and see whether there is a rel='nofollow' in the link. The other way to check it is using the nodofollow firefox plugin.
You better to follow blog guidelines,as well as you don't put link in Blog content.you better to use your link in Blog signature.
Anchor linking in the blog commenting will help for sure, but most of the blog owners (Adminstrators) will not appreciate anchor linking in comments. google also counts anchor links as back links. Relevant back links from the niche category will also helps to boost your rankings in SERP's.