I know you won’t extract tannins when your temperature goes over 170 if you keep your pH in line (e.g., when decoction mashing).
Would you extract tannins if your pH was high, but your temperature was below 170?
“Tannins” is a pretty broad class of compounds. Some tannins are a normal part of beer flavor and body. Excessive tannins could be perceived as astringent.
You definitely run a risk of overextracting tannins when either your sparge temp is too high, or if your sparge temp is lower but your pH is too high.
Get the mash pH set in the desired range 5.2 -5.6 or so.
Adjust the sparge water to the same pH using Phosphoric Acid (what I use) or Lactic Acid.
Then there are no worries.
Yeah, excessive tannin extraction leading to astringency was what I was getting at.
I’m not having an astringency issue, I’m just curious as to whether high sparge pH on its own causes a problem since it seems that high temperature by itself does not.
High temps and pH will extract tannins. I’m not sure about high pH and low temps but my guess is that it will but to a lesser degree. Your best bet is to avoid that situation if at all possible.
Based on my own experience, I’d say yes. Even keeping my temps in line, I found that my dark beers were harsh until I started paying attention to my pH.
Some say brewing is all about time and temperature. I say pH should be in there somewhere. 
pH is a factor, but only to the degree that it indicates that the water alkalinity is brought down. Alkalinity is the real factor that is the concern in reducing tannin extraction along with temperature.
For brewers that have brewing water with really low alkalinity, they don’t really need to adjust the sparge water pH. In addition, with a low alkalinity water, it would probably only take teeny amounts of acid to drop the pH anyhow.