If this is true, it is news to me, although a couple of points are worth mentioning.
Even if a CRA can freeze your report until a pending dispute is settled, they are not able to freeze your FICO score. A FICO score is generated on the fly when a report is pulled and that report is run through the FICO scoring algorithm. FICO scores cannot be frozen, because they are not generated until they are requested, and the only data used to generate that score is the data on the report at the time it is pulled.
So, assuming for a moment that a CRA refuses to update the report with new information while a dispute is pending, they still cannot stop the passage of time, which does affect one's FICO as accounts and baddies age. A single report containing the exact same data, pulled twice, thirty days between pulls, will likely generate two different FICO scores.
Also, it seems to me that if freezing a report also includes refusing to allow baddies to drop as they age off, this could very easily lead to FCRA violations regarding the reporting of obsolete information.
One tidbit that is somewhat related to the question at hand: When an item on a report is disputed by the consumer, the CRA is obligated to mark that item as disputed until the dispute is resolved. For FICO scoring purposes, disputed accounts are ignored while they are in dispute, with the exception of collections and public records.
I'll see what I can find out about CRAs freezing reports and post back here.
