Is discovery such as this permissible in small claims and would anyone recommend it as a substitute for proof?
The purpose of discovery is to develop evidence. The by-product may have more or less probative value than some other evidence, but it is “proof”. It’s a good thing and a good idea. Whether it’s available to you is the issue. It’s not.
Your Small Claims actions are governed by your Justice Court Rules of Civil Procedure. You can read them here:
Justice Court Rules of Civil Procedure
Note that Rule 2 distinguishes between civil actions and small claims actions. Rules 3 through 87 pertain to civil actions and include the discovery rules. Rules 88 through 100 pertain to small claims and don’t provide for discovery. Precluding discovery in Small Claims is the majority position. It would be likely to make an informal, expedited proceeding protracted and cumbersome.
Rule 1 allows the court to make special orders in the interest of justice, but you’re swimming against the current to try to get the court to incorporate formal discovery for the reason given.