No, you must choose one or the other as the preferred installation. It is not permitted to use both while in harness mode. In booster mode, however, the LATCH (UAS) may be used in conjunction with the vehicle seat belt. The LATCH will hold the seat in place when it is unoccupied.
If you’d like to find out more about the Diono Radian 3RXT visit our store: https://store.diono.ca/radian-3rxt/