Here in Texas, of course, it is much more accepted. In fact, Texans will warm up when I say 'howdy' if they are pre-disposed to thinking of me as a foreigner on account of my race. When I leave Texas I plan to continue to hang onto my Texas heritage. Perhaps I will even make people call me Tex.
"Howdy" used to the the only greeting in Aggieland. "Howdy" would get you face time with any number of pretty girls, who would say "Howdy" back - usually with a smile. I went back after 10 years of being gone and did not recognize the place with all the shoe-staring mumblers dragging their backpacks across the campus.
"Howdy" will - in some cases - get you a job with the older alums who have their own "bidness".
I've never been to Texas, but I will use "howdy" sometimes. It definitely sends a message that you're not one of the "Sup [dude/dog/man/yo]" crowd. Note that "Sup" or "tsup" is much different from "whatsup". I also use "what's happening" a lot. Occasionally in a Lumberg, if I'm at work, but not always.
You gotta change it up to keep life from getting dull.