Oshimaya (a Japanese NetBSD user on Twitter) uses Wacom tablets. It's supported by Xorg rather than OS-dependent drivers - X has some advantages...
The same person also uses a Dynabook laptop with a built-in digitiser. The older tablet series of thinkpads (x220t, x230t) also come with pens and digitiser displays - surely a must-have item for any BSD user give the already stellar support for that laptop generation in free software.