A debt collector can report their collection to the CRA at any time after they obtain collection authority, including prior to sending any notice to the consumer, unless they are under a cease collection bar.
They could have reported prior to sending you the initial collection ("dunning") notice, so no, they are not barred from reporting their collection.
The statement that you have 30-days to dispute the validity of the debt is a standard requirement in any dunning notice (see FDCPA 809(a)), and does not preclude reporting during that period. Many debt collectors will not report until after the period for requesting debt validation has expired, but they are not legally precluded from doing so.
If you do send a DV request within that 30-day period, it then imposes an automatic cease collection bar on the debt collector, which remains in effect until they first send the requested debt validation. See FDCPA 809(b).
If you send a timely DV, case law interpretation in most states has held that reporting to a CRA then becomes a violation of the cease collection bar, so if they have not yet reported and you send a timely DV, you will likely bar reporting until they have first sent validation.
Howver, they can send validation immediately upon receipt of your DV request, and then report the same day, so any bar in reporting is only temporary, and beyond your control.