I think the most important rule in terms of what rules govern a reporter’s use of good material discovered on a social media website is to make sure the source is credible.
For example, when I write my blogs I know which reporters to look for in order to determine what news is most reliable. Most of the time people will know who to trust and what outlets to trust based on prior knowledge. For myself, I know to trust Ian Rapoport because he has long been identified as the one of the best NFL insiders to provide breaking and factual news. Also, it helps to know who is verified and who is not verified online when determining sources.
To me, there’s no harm in “friending” a source to receive additional information from them. I follow many reporters and outlets that I get my news from on Twitter. However, the relationship should be strictly professional unless certain circumstances (family, life-long friends, etc..) come into play. As always, the information you take from that source should always be credited. With that, there shouldn’t be a limit as to how often you use the source as long as you do so correctly.
In my own experiences there are, however, rules regarding publishing material obtained from social media. I can’t just use anyone’s tweet to plug into my article for video, photos, stats, etc.. FanSided requires me to use verified and/or original material that was posted online. That way I am able to give credit to the source (person or outlet) while doing so with credibility by not posting a tweet from a third party.