No, there's no nickel added to Spiegelau glass. Yes, they are more durable than they appear.
From the presentation I attended last year by one of their reps, the glass they source starts "unusually pure" from the mines. The "blue/ green" tint that is seen in some "colorless" glass (like a standard pint glass edge-on) is an effect of impurities. On a molecular level, those same impurities also encourage lots of crystalline layers which are weak-points on impact, thus high quality Riedel or Spiegelau glass is actually stronger than 'standard' glass while also having improved qualities in lightness, clarity, and thinness, which effects liquid delivery and heat transfer from glass to liquid.
Check here under "superior glass differences" for microscopic comparison shots.
You're right, Spiegelau should've offered me a gig.