Yes I am sure and no that is not quite all that the ZHA integration page says so that might be confusing.
Fact is CC253x is not recommeded for production in ZHA regardless of firmware. Z-Stack 3 on CC2531 with zigpy-znp is experimental, but so is Z-Stack Home 1.2 with zigpy-cc, and zigpy-znp is more stable.
ZHA integration page https://www.home-assistant.io/integrations/zha/ list Texas Instruments based radios with Z-Stack Home 1.2.x (via the zigpy-cc library for zigpy) under “EXPERIMENTAL SUPPORT FOR ADDITIONAL ZIGBEE RADIO MODULES”, meaning that Z-Stack Home 1.2.x with zigpy-cc is not recommended for production with ZHA.
Though under “KNOWN WORKING ZIGBEE RADIO MODULES” it lists Texas Instruments based radios with Z-Stack 3.x.x (via the zigpy-znp library for zigpy) and if you follow the zigpy-znp link instead of the Zigbee2MQTT link you will find https://github.com/zha-ng/zigpy-znp project readme file.
Now if you read the whole of https://github.com/zigpy/zigpy-znp/blob/dev/README.md it says that it supports both Z-Stack Home 1.2.x and Z-Stack 3.0.x on CC2531, however, it also says that Z-Stack Home 1.2.x support on CC2531 is classified as “Alpha” (meaning experimental) and Z-Stack 3.0.x on CC2531 on is classified as “Beta” (meaning more mature than experimental but not stable enough for producion).
If you continue to https://github.com/zigpy/zigpy-znp/blob/dev/README.md you will see that you can do a backup and restore to other hardware as long as the firmware is the similar versions, which means that you can start out with CC2531 hardware with Z-Stack 3.0.x firmware and later upgrade to CC2652 hardware with Z-Stack 3.x.x firmware if you do a backup and restore.
As you also noticed Zigbee2MQTT on the other hand (which is not the same ZHA) recommends Z-Stack Home 1.2.x firmware on CC2531 and CC2530 but you need to understand that their recommendation is for Zigbee2MQTT and not for ZHA. ZHA only links to https://www.zigbee2mqtt.io/information/supported_adapters because that project provide firmware image files, however that does not mean that their firmware image files only work with Zigbee2MQTT, as it happens, they also work with ZHA (both with zigpy-cc and zigpy-znp).
Again, the main point you should take out of this is that CC2531 is still not recommended for production, but if you want to continue using CC2531 with ZHA when upgrade to Z-Stack 3 and switch to zigpy-znp.