The problem with many sites (and LinkedIn in particular) is that they whitelist a bunch of specific websites, presumably based on the business interests, but disallow everyone else in their robots.txt. You should either allow all scrapers that respect certain load requirements or allow none. Anything that Google is allowed to see and include in their search results should be fair game.

Here's the end of LinkedIn's robots.txt:

User-agent: * Disallow: /

# Notice: If you would like to crawl LinkedIn, # please email whitelist-crawl@linkedin.com to apply # for white listing.