Almost certainly it's from すねる + ぐれる. Because there is no in-between て, すねぐれる sounds like it's an established compound verb (such as 飛び起きる, こぼれ落ちる, 遊び呆ける), but I haven't seen this combination before.
From what I could google, it probably is a rare dialect word used in the eastern part of Japan.
This page lists すねぐれる as an 茨城弁 term.
There are a very few actual occurrences of すねぐれる/拗ねぐれる in some sites, for example:
And there are at least three native speakers who wondered what すねぐれる means, just like you.
As for your extra question, it's a simple result of 連濁 phenomenon. ～ぐらし is relatively common (eg, その日暮らし, 一人暮らし).