DRE is legit and 1st class. I got to meet them at PRI and talk to them. There diaper is NHRA approved. I know this because the tech guy at the NHRA booth sent me around the corner to see DRE.
Per this years rules, it is RECOMMENDED and NOT REQUIRED. The only time you are required a NHRA APPROVED diaper is 7.50 or faster which is advanced ET, comp, S/C and S/G racing. The SFI tag is not mandatory until you hit the alcohol and up classes. However, you should consult your home track or any place you plan to race. I know that as of right now, Norwalk( Summit Motorsports Park) required SFI approved on cars running 9.99 and faster in Super Pro and Comp.