Sitemap question

We have an SEO company telling us the first line in our robots.txt file should be this.

Sitemap: http://hearingfirst.org/sitemap.xml

They're also saying that the unconventional sitemap URL of sitemapindex.ashx is not search friendly. So I have two questions. Are there any ramifications if we add that to our robots.txt file, why did Telligent omit it if it is a best practice (if indeed it is a best practice...or does it not even matter), and would there be any drawbacks of having a redirect rule that sends sitemap.xml to sitemapindex.ashx?


Thanks!