If it's anything like the parachute operation I'm familiar with, IFR operations and dropping through cloud are permitted, the decision to conduct any particular flight IFR or VFR comes down to the pilot carrying out the flight in question on the day. This operation hires pilots with an instrument rating for this purpose. So for the conditions you're reporting, as long as the flight was planned IFR or upgraded to IFR in flight based on the conditions, and the cloud base was sufficient to meet the requirements in the approval to drop through cloud, it sounds legitimate. Why anyone would want to see virtually nothing while getting drenched plummeting earthwards through what feels like a firehose spray is another question, but skydivers are a strange bunch
