I am EXO-L, Shawol and SONE and from my perspective it looks like this.
(I hope everything will be understandable as my English is not very good)
I think SM separated EXO from the rest of the groups (especially the g-groups) in 2015-2016 when there were dating scandal from Krystal and Taeyeon. Before, they had tons of integrations with other SM idols. I have the impression that it was largely influenced by the behavior of the EXO-L themselves. Before 2015, EXO and SNSD had a lot of collaborations and integrations.
EXO has little integration with other SM artists, but when there are any official integrations, SM idols get hate for it, because "SM wants to promote another group through EXO".
Taeyeon saw the musical Suho and posted a photo of him on instagram, but had to remove it because she started getting death threats. Taeyeon often posts photos of other SM heroes and promotes their comeback on instagram, but I remember that only when she posts something related to EXO does she get hate.
Recently, SJ, on the tenth anniversary of EXO, greeted them and they were cheated for it.
SJ, on the 10th anniversary of EXO, sent them greetings and congratulations but they got hate for it.
When Karina appeared with Kai in the ad, it was cheated (EXO also had a lot of commercials with other SM artists during their debut, but there was no such hate on them from other SM fandoms.)
The MV reaction videos were the brainchild of SHINee and SHINee's managers. During the promotion, DCM asked other artists if they would record a reaction to their MV. Then some groups started doing this too.
Also it was with the tiktok challenges. HYO started doing this in SM. When she saw an artist (even when she just saw him in the SM building), she asked if he would dance with her. Then other groups started doing it too. a few LSM tiktokos started with HYO. The LSM asked for it, he agreed, and then several other groups did as well.
I think EXO has a lot of friends in SM, but often doesn't show it in public.
They had a program together
Xiumin and Mark from NCT
Mark got headphones for his birthday from Xiumin. "Young & Free" was Xiumin's idea. He wanted a song with MARK.
Suho and KYUline
Suho and SHINee (lived together before his debut and was due to make his SHINee debut)
Sehun has a lot of friends, but we usually learn about it from others, e.g.
Lai Kuan-lin (Wanna One)
Johnny (Johnny is friends with all EXO members and was about to make his debut with them)
Shotaro (NCT) - Shotaro and Sehun were seen together in a restaurant and Sehun was surprised that Shotaro made his debut
Donghae (SJ)
Kai and The Padding Squad (Wanna One and Hotshot's Sungwoon, Shinee's Taemin, BTS 'Jimin, Vixx's Ravi and Hotshot's Timoteo).
Baekhyun and Heechul (SJ) and Taeyong (NCT)
Playing games together.
Chanyeol and Yaesung (SJ)
As there are SMTOWN concerts they often go together,
Yaesung asked Chanyeol to participate in his album (Confession)
