Can I use the block drain for a temp sender?

I guess the first question is, is there a well/cavity there. Temp senders do have a probe end reaching into the water. Some aftermarket temp senders are too long for the correct intake location.
Of course the water would be hotter there, like oral thermometer versus rectal thermometer. OEM temp sender reports a general/average water temp. The water jackets around cylinders would read significantly hotter.