Can I erase an iPhone/iPad that does not allow pairing with a host PC by connecting it to a computer?

If Allow pairing with non-Configurator hosts is set to OFF in the profile, you cannot erase the device even if you connect it to a computer.
You need to put the device into recovery mode and then connect it to the computer.
For how to put the device into recovery mode, see here.
For how to erase the device, see here.