Wrist tattoos and workout pause…

While fieryjack's quote from the support article is correct, there have been anecdotal reports of people wearing the watch on the inside of their wrists and finding the results acceptable. You won't damage anything by trying.

Wearing your Apple Watch - Apple Support

No,

Quote from apple support page "how to wear your watch";

You may want to tighten your Apple Watch band for workouts, then loosen

it when you’ve finished. In addition, the sensors will only work if you

wear your Apple Watch on the top of your wrist.