DNS just translates URLs to IP addresses. I don't see how it would help upload/download speeds once you've connected to a site, but a bad DNS server will make connecting to a site take a while. Slow DNS servers make it take longer to find the site, but once it's found, how would DNS matter?
This script requires you to run it with an argument telling it which ppp device to use, ppp0 or ppp1 (does android even use ppp? mine doesn't but it's a Nexus One that doesn't have anything added by any carrier). If you don't supply it with an argument, it won't do anything. It will skip the first half of the script and enter incorrect information in the second half.
(it tries to enter things like: "net.$NAME.dns1", the $NAME variable is the same as the argument you use to run the script. If you don't use an argument, it will enter "net..dns1")
The script is placed in /etc/ppp/ip-up, meaning it is supposed to be executed when the ppp daemon detects a ppp connection. I don't think the ppp daemon can run it with arguments.
I personally don't see how flashing this script would do anything at all.
Just open a terminal emulator and type:
echo "nameserver 18.104.22.168
nameserver 22.214.171.124" > /etc/resolv.conf
voila, DNS changed!