What do you mean by "does not appear to be the case"? I have those urls blocked, and the eShop works fine for me. Haven't tried online in a game yet, but the connection test in Settings completed successfully too.
I actually have the same concerns with my router - I was using the Tubehax DNS for the longest time and the eShop was always blocked, which I thought was the expected behavior all along - online play continued to work, provided that the software had not forced any updates, main offenders are usually SMM/XCX here - the fix would just involve disabling Tubehax briefly, pulling down the game update and then reenabling it. Not a big deal to do that since the latest firmware was considered "safe" but I'm sure this will all be changing soon.
Blocking these URLs in my router still lets the eShop be accessible so I'm worried that not everything is being blocked that should be (caveats of URL blocking in my ASUS RT-N66U is that https and compressed webpages are unblockable)