Few possible Vegapunk's research team or maybe connected to the research team or knew something about the research findings. This might not 100% true but maybe this could raise some possibility.
- Blacbeard - During the Marineford tragedy, Marco said that BB's body was not normal. BB's body structure was weird and maybe that is why BB could absorb WB's power. This could raise the possibility that BB was genetically modified and be able to hold two different kind of devil's fruit powers. BB also have the DF book which contains all different kind of DF that ever exist and their powers. This is not a common book that maybe only Vegapunk and Sanji had access to it (Suke Suke No Mi). Indeed Vegapunk put a lot of efforts in researching the DF.
- Dr. Kureha - In Punk Hazard, Chopper discovered the NHC10. Only a few scientist get access to this drug, like Ceaser and Vegapunk, so Dr Kureha could be part of the research team. She also has a superhuman speed, strength and be able to withstand against cold climate. She is also 141 years old which surpasses the normal human living age wtih tons of energy and not really affected with the age. This also could point to somekind of genetic modification and part of the research team.
- Crocodile - He is the first one to mention about the Awakening in Alabasta and he perfected his DF. He also pointed out the AWAKENED DF ZOAN in Impel Down. Other than that, certain DF can be countered by other DF according to Crocodile. This shows that Crocodile has a huge knowledge about DF. In Alabasta story line, Lassoo was introduced (a DF weapon) where Veagpunk only does for the WG and very hard for anybody else to have it. And if Crocodile have this kind of technology, he might be part of the research team. There are also some similarities between Crocodile and Germa.
If this idea is not in favor with you, just comment it politely. Thanks.