The SkyTeam rules on lounge access are very clear as regards business class tickets:
All international First and Business Class passengers traveling on or connecting to/from a same-day international flight operated by a SkyTeam member airline have access to our exclusive lounge facilities. Simply present your First or Business Class boarding passes for the lounge agent to validate for admission.
Lounge access is reserved for Elite Plus, First and Business Class customers flying on international flights or with same day connections to/from an international flight operated by SkyTeam member airlines.
International First and Business Class passengers, as well as SkyTeam Elite Plus members traveling in Economy Class, enjoy complimentary access to more than 750+ worldwide member lounges on the day of travel when flying on or connecting to or from an international flight operated by a SkyTeam carrier.
There's no small print that I can see.
However, the e.g. Air France rules on Business Light fares are also fairly clear, with some small print:
Access to our exceptional lounges*
Away from the hustle and bustle of the airport, enjoy the peaceful atmosphere of our Business lounges. Enjoy a personalized tour to discover the spaces and services available to you. Whether you choose to eat, work, get information about your flight, or simply relax, our lounges were designed to meet all of your unique needs.
*Except for Light fare tickets
So how does it work out? Is AF required to provide some lounge for people on a Business Light fare, just not necessarily the nice one (a bit like QR's tricks for oneworld Sapphires in economy)? Or does the AF rule somehow trump the SkyTeam rule? Or maybe it only trumps it for AF lounges, i.e. if there's a non-AF lounge then the SkyTeam rules do apply, but if there's only an AF lounge then no lounge access?