Actually, a ZR rating just indicates that they're good for speeds in excess of 149MPH.
Correct, but that's DOT's street rating. SCTA allows them to 200.
(Y) rating is "over 186 mph". Does that mean Bloodhound could run them at 1,000?
You're correct that the ratings I quoted are DOT's and that SCTA rules specify that ZR (and VR) rated tires are good to 200MPH. However, I doubt that SCTA did any actual tire testing to verify that tires with those ratings are good to the speeds quoted in the rules.
"ZR" is actually included as part of the tire size, such as "225ZR45-17", rather than the actual speed rating. The actual speed rating (V, W, Y, etc.) is shown separately, normally after the weight rating, e.g. "86W" (1168 pounds, 168MPH).
The numbers quoted by Tire Rack (or tirespeedratings.org) don't agree with what SCTA shows in the rule book.
Here's what I found:
RATING TIRE RACK SCTA
Q 99 100
S 112 115
T 118 120
U 124 130
H 130 150
VR discontinued 200
ZR >149 200
It looks like SCTA's tire ratings are a bit antiquated. Prior to 1991, the speed ratings were included as part of the tire size. For example, there were SR (112MPH), HR (130MPH), and VR (149MPH). Use of those three has been discontinued. ZR still persists, but only as part of the tire size, and not a speed rating. Since VR has been gone for over 20 years, SCTA may want to give the rules on tires another look.
SCTA's 150MPH rating for H-rated tires is suspect, too. USFRA won't even permit use of H-rated tires on the street cars running in their 150MPH Club.
As for Bloodhound, I doubt if it'll be running under SCTA rules.