That used to be an accepted way to grasp the violin in general, not just for fiddlin', right up into the 18thC.

The downside is that you have to hold it entirely and very firmly with your hand and thumb.
Your wrist now helps to hold up the instrument so it is in what a violinist would call a 'collapsed' position against the neck of the fiddle. This has several disadvantages:-

1.You can't do vibrato (so?)
2.You can't shift out of first position (so?)
3.It's harder to reach some notes because your fingers are pretty much locked in one position; so the keys of C, F, and Bb (and Eb too!) are harder, which is OK as long as you stay in G, D, & A.
4.Bow control is rougher because of your posture, leading to less good (or different!) tone control.
5.It's harder to do than you think! Those good ol' boys still practiced a lot and had talent.

In the end though, as long as you are prepared for the limitations, it used to be the normal way to do it, and it will be easier on your tinnitus.