Can I use 豿 as an ultra traditional variant of 狗？
Not really. The original is 狗， as seen in 说文解字 the great etymological work, Shuowen Jiezi (which people who haven’t studied the book like to criticize).
I read a lot of old books, and I love to read the old woodblock versions. I honestly don’t think I’ve ever seen 豿 used.
So I would say that 豿， rather than being an “ultra traditional variant” of 狗， is a corruption. The original was 狗， as seen on this late Shang dynasty bronze:
There’s your ultra traditional 狗。
But when it’s all said and done, I have to admit, 豿 does look pretty nice.