No, SIP is fully enabled on both the machine with the Developer Tools category and the one without.

Interestingly, I rebooted the machine without after some benchmarking and experimentation with syspolicyd (see https://news.ycombinator.com/item?id=23274903), and after the reboot the category has mysteriously surfaced... Not sure what triggered it. Launching Xcode? Xcode and CLT were both installed on the machine, but I'm not sure when I last launched Xcode on this machine. Another possible difference I can think of: the machine without was an in-place upgrade, while the other one IIRC was a clean install of 10.15.

In the worst case scenario, you can probably insert into the TCC database (just a SQLite3 database, located at ~/Library/Application Support/com.apple.TCC/TCC.db) directly:

  INSERT INTO access VALUES('kTCCServiceDeveloperTool','com.apple.Terminal',0,1,1,NULL,NULL,NULL,'UNUSED',NULL,0,1590165238);
  INSERT INTO access VALUES('kTCCServiceDeveloperTool','com.googlecode.iterm2',0,1,1,NULL,NULL,NULL,'UNUSED',NULL,0,1590168367);

(Should be pretty self-explanatory. The first entry is for Terminal.app, the second entry is for iTerm 2.)

Back up, obviously. I'm not on the hook for any data loss or system bricking.

> In the worst case scenario, you can probably insert into the TCC database

Does this not require disabling SIP?

Yes. I got mine to appear through mysterious yet fully SIP-enabled means, but if all else fails for you you can temporarily disable SIP to change this.