@phaedrux just tested, it seems so. I turned it to 250c overshot by 2c, waited a minute turned the fan on dropped a couple and it looks pretty stable now:
Please send an email to warranty@duet3d.com and CC your reseller. Include a link to this forum thread and the details of your original purchase. You'll receive a reply with a form to fill out.
I'll add a note to io5 and 6 to explicitly say endstops. However, one of the main features of the Duet 3 is the versatile nature of the IO ports compared to having dedicated ports for specific hardware. The only differentiating thing between 5&6 and the rest is tha lack of PWM output, so literally perfect for simple endstops.