Understanding DTM test setup

Hello,

I am using nRF52840 S140 v7.0.1. I have few queries on DTM functionality.

1) As per standards, we can do DTM test either by sending HCI commands or UART commands. Using HCI commands I can have 7 different packet sequence.

    Whereas using 2-wire UART interface, we can have only 4 different packet sequence as packet type is of 2 bits. Please current me if I am wrong in my understanding.

2) Similar to 2-Wire UART interface, whether can I send vendor specific commands over HCI. I am not seeing “Packet Type : 11” Vendor specific in HCI interface.

3) I am new to certification. Trying to understand concepts. Whether DTM test setup is for only Bluetooth SIG Certification or even for FCC certification.

4) For DTM test setup, I am seeing python scripts and setup detains in below link

              https://infocenter.nordicsemi.com/index.jsp?topic=%2Fstruct_appnotes%2Fstruct%2Fappnotes_nan34.html&cp=13_3

              Even in nRF Connect Desktop tool I am seeing DTM. Whether using nRF Connect Desktop, whether can I test DTM for certification. Is it approved to use or we need to use only Bluetooth SIG approved devices.

Thanks & Regards

Vishnu Beema