Do we have to insert the DC null in OFDM when using RF direct sampling ADC architecture?
RF direct sampling architecture?
Will there be DC offset?

No, since the center of your signal doesn't end up on DC, so there's no DC offset.

If not, then is it okay not to insert a DC null?

yes.
However, you might want to use quadrature mixers for the other end, so you might not want to do that.
Also note that instead of direct sampling, superhet / low-IF approaches can also get rid of the DC offset, as does, to a not-so-bad degree, calibration. The question whether you need to insert a zero carrier at the center frequency of your OFDM signal is often a complex, more systemic one than just looking at the receiver architecture.