At least in the United States, which is where SE is based, one of the primary justifications for fair use is education. As such, posting small portions of a camera's Instruction manual or User's Manual for the purpose of instructing someone on how to use the camera or other device for which the manual is written is solidly covered by the Fair Use Doctrine.
I can't imagine a camera maker objecting to posting a page or two from a several hundreds of pages document that helps someone learn to use a product they wish to sell to consumers. But even if they did object, at least in the United States, there's not much they can legally do about it.
As for the safety of links:
Everything on the internet carries a degree of risk. Even a link to this question can be unsafe if an unscrupulous entity has managed to alter a 'hosts' file on a local machine attempting to use the link or has managed to hack into a Domain Name Server and alter the resolved ip address in the database to redirect traffic to a nefarious site.
I can only speak for myself, but links to User/Instruction Manuals that are included in answers I post are usually direct links to a document provided by the camera manufacturer themselves or provided by a reputable seller of photographic equipment. B & H Photo, for example, includes links to instruction manuals for many of the products they offer. Sometimes these links seem to be hosted within B & H's own domain, at other times they seem to be links to one of the manufacturer's domains.
In cases of old and long discontinued products, there are a few sites that are well known to the photographic community to have a large collection of scans of old manuals. These sites, for the most part, are reputable as being above board and not hosting malicious code. YMMV.