Can I3C Hot-Join Target Devices be used on a Legacy I2C bus?

Only if they have a way to turn the Hot-Join feature off, or if passive Hot-Join is supported. (See Q17.7, "Can an I3C Target support Hot-Join when used on an I3C Bus, and still function correctly on a Legacy I2C Bus?")

Hot-Join Requests are not compatible with Legacy I2C controllers, so Hot-Join would have to be disabled for  the Target to be used on a Legacy I2C bus. The disabling of the Hot-Join feature should be done via some feature that is not part of the I3C protocol (i.e., not via the DISEC CCC), since an I2C controller does not support the I3C protocol.