But I’d like to think Numair wouldn’t keep what would essentially be a slave, whether created by him or othewise.
I can see it happening, if Numair didn't create Sraddi but discovered that Sraddi's sentient, or created Sraddi in Numair's youth without fully understanding the consequences: because the only way to protect Sraddi from destruction might be for Numair to keep them as if they weren't sentient, and Sraddi might not want to be destroyed and might accept living under Numair's protection in that fashion.
If that's the situation, however, I'd expect that whatever restrictions there are on Sraddi interacting with others, that Sraddi would be able to choose to override them. But they might not trust Hawk enough, at least yet, to do so. -- and I'd also expect that there are often conversations between Numair and Sraddi that we're not being shown.
-- however a considerably simpler explanation would be that Sraddi's just a non-sentient tool, and that scene was only meant to show something about Hawk's character.