Evangelical protestantism is a growth phenomenon many places, clearly due to religious conversion. Plenty of people in America with no other "southern" cultural or genetic ancestry are becoming evangelicals today all across the nation.
The notion you need some sort of Dixie ancestry to be attracted to an evangelical church seems pretty well put paid to by the massive expansion of the family of denominations in places like Latin America or South Korea!
So, by itself it means practically nothing in terms of gauging southern demographic spreading in the USA.
Meanwhile, it would be entirely possible for regions that have little or nothing in common with the American South to find their situation paralleling the Southern one in some crucial ways everyone thinks is most important and therefore to calculate that joining some ATL version of the Confederacy is what they want to do. To think otherwise is to buy into the post-Civil War racist whitewashing that held that that the OTL Civil War was fundamentally about an abortive bid for national independence of a separate Southron people and all that bull. Southern Americans are in fact part of the larger USAian culture and society; they have distinctions but the notion they were driven to secede by nationalistic incompatibilies is a clear case of whitewashing the true cause, which was slaveowner greed fundamentally. The slavocracy had little trouble considering themselves culturally compatible enough to run roughshod over the US federal government in the generations before 1860 right up through the previous Buchanan administration; they were just taking their ball and going home in a huff because their bid to dominate out of proportion to their population was failing at last. Similarly after Reconstruction via the "solid South" one-party rule which enabled Southern politicians to gain absurd amounts of seniority in House and Senate, the South again managed to hold power in the Federal Government out of proportion to population, the more outrageously so because now their African-American population was being counted in full to give them representation but not actually permitted to vote on their own behalf.
This generic open door to kindred spirit states or territories unconnected to the South is realistically a lot less open when we do recall that if shared cultural heritage is hogwash in this argument, shared institutions of slavery would not be. The only reason a lot of Southern fire-eaters thought secession was the necessary next step was to preserve their "right" to own slaves; no other issue could have been so very decisive. For Alaska or Hawaii to be attracted to the Confederacy, they would need to be dominated by slave owners.
If you made either so beholden, it would not matter how much or little cultural affinity there was between the sections, if the social structure were similarly shaped around slave ownership, they would be natural allies. Without slavery, either could be 100 percent settled by people from Georgia or Alabama or South Carolina, and if they differed from their motherlands in being resolved not to institute slavery, their shared bond would at most be a weak bond of sentiment; more likely we'd be looking at a region with as little loyalty to the Confederacy and as much to the Union as West Virginia. Post war, who knows, but in the Civil War period they'd be Unionists, unless the specific reason a contingent of settlers from the heart of Dixie was promoted was to lay the groundwork for introducing slavery there and the white voting population was on board with that.