Sumner Shearman doesn't mention anything to this effect in his memoirs. He was a captain in the 4th Rhode Island Volunteers (9th Corps, 2nd division) and entered the 'Crater' in the second wave, after Ledlie's 1st division had bogged down. The 30th USCT followed in the third wave, being in the third division of 9th Corps. I find it hard to credit that such an incident occurred and Shearman glossed over it. He was in the 'Crater' when the USCT troops came up and succeeded in occupying Cemetary Hill for a short while. He states also that before the troops stuck in the hole surrendered, an order to withdraw was issued, presumably by Burnside.