K90 controller described a potential conflict event between IFR and VFR traffic; the IFR traffic given avoidance vectors.

Narrative

Aircraft X checked in. I observed a VFR target 8 miles north of Aircraft X; proceeding southwest bound toward ACK; indicating 2000. I asked for flight conditions from Aircraft X. He responded IMC. I issued an immediate climb to 3000 and a right turn heading 360. I issued traffic; 12 o'clock; 5 miles same altitude; opposite direction; indicating VFR. The collision alert sounded. The aircraft involved were separated by approximately 3 miles; the VFR target indicating 2000; Aircraft X indicating 2100. Target beacon; primary returns merged. Vertical separation at this time approximately 300'. Aircraft X reported traffic in sight. Once separation was increasing; I descended Aircraft X to 2000 and issued a left turn heading 340 for the VOR Runway 06 approach. Aircraft X called the facility and requested to speak to me. He was upset that; given the vicinity of the situation and the prevailing weather conditions; the conflicting aircraft was attempting to operate under VFR. I explained that both his departure airport; as well as the ultimate destination airport were reporting VFR condition. Thus; The VFR aircraft was authorized to conduct his operation and no rules were broken. Aircraft X was appreciative of my service; yet remained upset that the conflict VFR aircraft conducted VFR flight in what he described as IFR conditions.