If two strings of equal length from random offsets in Pi were XORed together, would this result in a cryptographically secure random number suitable for use in a one-time pad? If so, would this mean that using a secure low-bandwidth channel, you could bass three digits (two offsets and a length) to provide an arbitrarily long pad?
There's no benefit whatsoever to using XOR here. Pi is already believed to be Normal which means the stream of digits is indistinguishable from random in every base.
The offset into Pi functions as a key, for your system to be secure this key must be very large (e.g. several dozen decimal digits long) and chosen entirely at random, and it must not become known to anybody except the communication parties. With those constraints you should just use a stream cipher which is intended for this purpose.
If you just believe that "Nobody" would guess that your "three digits" are the key to a cipher based on Pi and so it's safe to just transmit the key to the other party you're relying on Security by Obscurity and might just as well use mirror writing or pig latin or something.