Is it legal if I distribute Ventura 13.0 beta 1 to a beta tester?
No, it is not, read the legals: https://beta.apple.com/sp/betaprogram/legal
3. License Grant and Restrictions. Subject to your compliance with this Agreement, Apple hereby grants you a personal, limited license to use the Apple Software on Apple-branded products solely for testing and evaluation purposes and only in connection with this Beta Program. Except as otherwise permitted under Section 15, this license does not grant you the right to use the Apple Software for any other purpose, or to disclose, reproduce, distribute, modify or create derivative works of the Apple Software. You agree not to decompile, reverse engineer, disassemble, decrypt, or otherwise attempt to derive the source code of any Apple Software (except as and only to the extent the foregoing restrictions are prohibited by applicable law, or to the extent as may be permitted by licensing terms governing use of open-sourced components included with any such Apple Software). Unless otherwise permitted under Section 15 below, you certify that the Apple Software will only be used for testing and evaluation purposes in connection with the Beta Program, and will not be rented, sold, leased, sublicensed, assigned, distributed or otherwise transferred. Apple retains ownership of all Apple Software, and except as expressly set forth herein, no other rights or licenses are granted or to be implied under any Apple intellectual property.
Why do you need to distribute ? Why not just ask tester to download ?