Outside of the hybrids, fossil Pokemon actually do very well and adapt easily. They’ve never known any other world, and the most important thing is making sure their trainers can meet their very specific needs. For the hybrids though there are plenty of examples:
We have used Arcanine to help keep Arctozolts warm at the facility I’m at. They loved to cuddle, and the Arctozolts loved a way to stay warm. Arcanine’s playful nature also helped to encourage the Arctozolts to move around and stay active and not just huddle down and shiver.
Arctovish do very well when paired with Seel or Dewgong. They’re social, playful, and smart Pokemon– meaning they can be easily trained to bring food to Arctovish’s mouths to help them eat. They do well in cold waters, their horns can break apart the ice, and the Seel line will be quick to alert their caretakers if Arctovish begins to struggle with breathing.
As you mentioned, there is Dracovish with Araquanids, but any Pokemon that is experienced with water manipulation (typically those with the Water Veil ability) can help Dracovish breath, and help teach them water manipulation for themselves.
And a bit of an opposite to your question, but Dracozolts actually make very good adoptive parents and can help incubate eggs. They have strong maternal instincts and aren’t picky about who they mother, making them great choices to help care for orphaned Pokemon.