DanceVision is now certifying teachers. If you take a DVIDA examination I believe you have to register as a member of NDCA (National Dance Council of America???).
The DVIDA syllabus matches the ISTD syllabus but there are some interesting variations.
With DVIDA you can certify in one dance at a time only if you wish where ISTD is comprehensive.
An Associate in ISTD requires waltz, tango, foxtrot, quickstep theory and technique plus a demonstration of beginning social foxtrot (American style). DVIDA ups the bar requiring Viennese waltz at Associate.
ISTD requires men to dance their part in a couple as leader but have the option of demonstrating the follower's part without a partner. DVIDA requires male candidates to dance both parts with a partner.
DVIDA also certifies American Style while I don't believe ISTD does (I could be wrong).
ISTD is older and worldwide where DVIDA would appear to be privately held primarily in the USA. As such some would view an ISTD certification as more prestigeous.
The Victor Verasset & Heather Smith are a great resource and I use them. However, they do not describe everything like footwork, alignments, amount of turn, etc. in the grey book required for the exam. DVIDA has put out an exam prep DVD with Diane Jarmalow. It's useful but expensive ($170??)and not comprehensive. Best for exam purposes are the Elizabeth Romain videos put out by ISTD. They are also expensive.
Hope this helps.
OB