After other recent questions, I'm more aware than ever how much research NASA has documented, and how much interplay there is between its many facilities and huge staff, and private aerospace enterprises. So how much is that data tapped, and by how large a group of people? Is it enough to be a student at an accepted institution? Do you have to register yourself or request it some way? Is it a hard rule that only Americans can get access to the portion that isn't public?
Generally speaking, NASA documents aren't classified and are available to the public on request -- although they are subject to International Traffic in Arms Regulations (ITAR) restrictions. This doesn't restrict many documents, but verifying this can slow release. Many times, something has to be requested before it is made available online.
NASA has lots of its materials online: NASA Documents Online (http://www.hq.nasa.gov/office/hqlibrary/find/nasadoc.htm).
From the summary:
The following is a list of NASA publications that have been put online in either full-text or hypertext format; also included in this list are some frequently requested non-NASA documents. This page will be updated as often as possible and we welcome your comments. If there is a NASA document you are looking for and cannot locate it here, try searching the NASA Aeronautics and Space Database, its public version the NASA Technical Report Server, our library catalog NASA GALAXIE, and the Johnson Space Center Document Index System, or NASA Headquarters employees can request a search.
The NASA Scientific and Technical Information (STI) Program has a nice twitter feed of document releases at https://twitter.com/nasa_sti.
Regarding their role in private aerospace ventures: I'm not sure what you are asking for.
I can also not provide a reference that described the direct influence this had on the development on commercial rockets, but I find the NASA technical report system to be a very valuable source for this kind of information:
This website includes the database that briligg linked to in her comment as well as two other NASA databases.
The US taxpayers pay for these developments, so they are entitled to seeing the results. And once something is published within the USA, its futile to try to keep it out of the hands of other countries' citizens. Better to release it publicly to make a showing of generosity and technological leadership.
By the way: Russian textbooks on the topic are just as freely available and cover the topics in a similar degree of detail. Often, they are more up to date.
I would offer as an answer regarding the use of NASA research by commercial space firms, that the Merlin engines use a pintle type injector in the combustion chamber. The Apollo Lunar Excursion Module used a pintle injector in the descent engine. Pintle design is a lot different than plate injectors traditionally used. Such design allows for thrust modulation over a 10:1 ratio. This design was analyzed and tested extensively by NASA in a major effort for the Apollo program.
It seems unlikely to me that SpaceX could have replicated or redone from scratch all the massive effort that went into the LEM Decent engine pintle injector design. It is more likely that SpaceX simply scaled the design based upon the NASA work efforts.
The LEM descent engine used storable propellants (A50/NTO) and Merlin uses LOX/hydrocarbon (RP1) so additional analyses and testing was necessary, but there was a massive amount of reports from NASA to be used as a starting point.
It seems unlikely to me that SpaceX would have come up with the concept of a pintle injector approach at all without investigating the NASA Apollo efforts and having that data and analyses available.