After reading this article about some Legends content still being produced, along with the SWTOR still being available to play, does this mean that content can be added to Star Wars Legends (such as if it does not fit in currently with the new canon)?
You've answered your own question: Star Wars: The Old Republic, the BioWare-developed online game set in the Knights of the Old Republic continuity (ergo, Legends1) is still being actively developed, and has received quasi-regular story updates since the (April 2014) canon reorganization, as recently as November 2017. So not only can new Legends stories be told, they are actively being told, at least for now.
Similarly, other licensed products have mined Legends for material; we have another question on the site about one of Fantasy Flight's war games, and at least one of the licensed mobile games has incorporated popular Legends characters.
...but don't expect them to
In principle, Disney/Lucasfilm can do whatever they want with the Star Wars canon; if they wanted to continue Legends storytelling, there's nothing preventing them2. Whether or not they will is a different matter, and seems unlikely; the New Republic Historical Office (an EU-advocacy fan group) report on a letter from Lucasfilm, received in response to a letter-writing campaign asking for a return to Legends continuity, which emphasizes Lucasfilm's commitment to the new storytelling:
Since Lucasfilm joined Disney, Star Wars storytelling has been delighting fans, expanding the Star Wars mythology across diverse mediums in new and exciting ways. During this unprecedented era of expansion, our focus is on creating and building upon the new Star Wars stories.
Lucasfilm is certainly not averse to releasing non-Canon content, but there are no immediate plans (none that have been made public, anyway) to continue Legends storytelling outside of The Old Republic. Even SWTOR is an anomaly, and appears to only be ongoing thanks to the multi-year licensing deal between Disney and EA (BioWare's parent company). Difficult to see, the future is, but there's a very real chance that all Legends development will end once that deal expires.
1 That SWTOR is a continuation of Legends storytelling was confirmed by Lucasfilm Story Group executive Pablo Hidalgo on Twitter. Unfortunately I seem to be unable to search his tweets, or link to them directly, but some pop culture reporters discuss the Tweet on their Facebook page. In case the links ever start working again, the original tweet can be found here.
2 There may be some legal implications involved with continuing stories that were created by third-parties under licenses. Or there may not be; I'm not a lawyer. Even if those problems exist, however, they're not insurmountable; with enough time, money, and lawyers (and Disney certainly doesn't lack for at least two of those), anything is possible
Perhaps this would be better left for a comment than an answer...but my expectation would be that if they wanted something from Legends, they would simply use the Grand Admiral Thrawn approach.
For those unaware, Thrawn was a character introduced in 1991: a high-ranking member in the Imperial Navy, he and his forces emerged from the obscurity of the galaxy 9 years ABY in an effort to consolidate the remains of the Empire's power and crush the New Republic.
Leaving the rest of the story to your own research, he is one of the most beloved characters from Legends, at least of the bad guys. When Disney bought Lucasfilm, his existence, along with everyone from Legends, was called into question. Much to my delight, he was re-introduced into canon via a new novel by Timothy Zahn (his creator) and, again to my delight, as the primary antagonist in the last couple of seasons of Disney XD's Star Wars Rebels TV show, and IMO is an excellent and fairly faithful representation of the original character.
Surely other characters will be brought back, but I would refrain from speculating on who, and I would doubt that they would continue with the same storyline, instead opting for a new one. I assumed Mara Jade would be brought back at some point, but it looks unlikely at best at this point.