Hey. Did anyone actually go into training mode to test any of this, or are you all just saying things that sound right? Went into training mode. Big Band's SSJ does not punish on block (unless there's a bug with setting Big Band to super on reaction). No super does (checked US, Fenrir, SSJ, the fastest supers afaik). The only thing that seems to punish is PBGC the first hit, but even still it looks like only Big Band and Squigly can punish with SBO and SSJ (works midscreen). There may be a couple characters who can PBGC super if your back is to the wall, but putting this at the end of a blockstring will give the distance you probably need to still be safe (didn't check, but anyone else totally can).
Bottom line, unless their name is Big Band or Squigly, them blocking the first hit of Spiral means, yes, you're safe. Put lk spiral at the end of every block string and laugh when they mash super.