There's no real evidence for any of the Arkentools as conscious entites. But, as you state above, the character bio states the Hammer likes Stanley, which is evidence of discernment*.
I forget, do we have Word of the Titans that the cast page was even canon?
My portrayal of the Tools being sentient was based on my memory of Rob discussing the character bio in terms of it being true canon, and confirming that "Tools are people too". However, looking everywhere I can think of, I cannot find this conversation to quote, so maybe it was my faulty memory ascribing the certainty of Tool sentience to Word of the Titans, when perhaps it was merely another forum speculation I read.
That being said, I stick to my point about "who can attune Arkentools?" speculation being moot, because I interpret "attunement" to be merely a manifestation of a particular Tool's choice. That's not a new stance for me...In the very early days of Book 1, before we had the benefit of separate Erfworld forums, the very first tinfoil hat theory I ever aired, before we had the insights into the characters that we now do, was the idea that the reason things were unfolding as they were (the RCC I set in motion, Stanley feeling compelled to conquer, Charlie getting involved, etc.) was because the Tools were working toward some unknown goal, putting their wielders on the move.
Some of my reasoning may have been flawed or wishful thinking, like any good TFH theory, but nothing has happened throughout this whole time to deny it's possibility. Makes me all warm inside just thinking about it. lol