Nuttso I can't find any reference that the Pixel 7's Arm 8.2 supports MTE functionality. It appears that some MTE functionality exists for Arm v8.5+ with "full" (or mature) functionality in Arm v9+.
It appears that Arm v8.5 introduced MTE and ABI, which is a way for the system/OS to inform the bootloader to override its default MTE configuration. (I think)
Armv8.5-A incorporates a new feature called Memory Tagging.
If Arm v8.2 (Pixel 7) does in fact support some MTE functionality, then in theory (I am not an Android developer), the Pixel 7 should be able to have MTE enabled by the GrapheneOS developers through its build configuration. However, the Pixel 7 will likely lack the ability for an OS settings toggle due to the lack of the ABI capability (introduced in 8.5).
In Android 13, Google added an ABI for the userspace to communicate the requested MTE operating mode to the bootloader.
An additional feature in Arm v8.7-A, Asymmetric MTE mode provides synchronous checking on memory reads, and asynchronous checking of memory writes, with performance similar to that of the ASYNC mode.