I think it was in danger a few times - Both bouts against HBK and HHH, the first one against Kane and both times against Batista and Randy Orton.
But i do believe had Hulk Hogan faced Undertaker at 7/8 or 9 - The streak would be totally non existent today as ya know what his ego was like at this time!
Undertaker won in his first match against Hogan, ego had no part.
Hogan had some respect for Taker obviously, Hogan has never cleanly beaten Taker yet Taker had beaten Hogan twice both times for the world title.
Why would Hogan had faced Taker in Takers first WrestleMania?
that rules out 7 plus he wanted 7 to be against Sgt Slaughter and it finalised the US vs Iraq/Iran situation in the WWF, 8 was meant to be against Ric Flair but it never happened and 9 he wasn't even gonna be there.
Meanwhile Taker didn't even have a streak in the books at that point it was just 3 wins by WM 9.
Realistically Takers first threat was Giant Gonzales at WrestleMania 9, Gonazales had his number until he decided to suffocate Taker cause a DQ that was never actually announced.
Since then there's several people that took him to the absolute limit and the possiblity was there that they were pulling the plug.
In story
Triple H twice came within a split second, HBK could've done it, Diesel nearly did it, Batista came the closest in years at Mania 21.