[pxeger1]

Companies have to be seen to be enforcing their trademarks, or they risk losing them. (AIUI, IANAL)

Although again if it were handled by marketing, might they just agree to licence the trademark to this person for this specific purpose for a nominal sum?

[deelowe]

Not quite. They simply must be seen as actively using the trademark. Simply sending the domain owner a notice with strict rules describing how to avoid trademark confusion would be enough to show ARM has not relinquished it's mark. There is no requirement that they must aggressively go after people like this.

[jpgvm]

Or just adding a notice to the site that `Arm is a registered trademark of Arm corporation` or similar bullshit which gets exactly the same job done.