I don't know all the details of any of the competitors you listed...they could have been suspended from the NPC before returning to compete there, they also may not have been competing for anything but a trophy in a different federation, which is not a problem...
Shiloe Steinmetz
2003 - Pro Galaxy - NGA, 4th
2003 - Natural Olympus - NGA, Professional Overall Winner
2004 - Pro Natural American - WNBF, 6th
2004 - Junior Nationals - NPC, Light-HeavyWeight, 12th
2004 - North American Championships - IFBB, HeavyWeight, 12th
...
2007 - Junior Nationals - NPC, HeavyWeight, 8th
2007 - Team Universe Championships - NPC, HeavyWeight, 1st
2007 - World Amateur Championships - IFBB, Super-HeavyWeight, 15th
clearly no suspension or time between being a pro and competing in the NPC there
Richard Tricky Jackson
1998 - North American Championships - IFBB, LightWeight, 1st
1998 - Team Universe Championships - NPC, LightWeight, 1st
1999 - Musclemania, Professional, 7th
1999 - Nationals - NPC, LightWeight, 2nd
1999 - Team Universe Championships - NPC, MiddleWeight, 3rd
2000 - Musclemania, WelterWeight, 1st
2000 - Nationals - NPC, LightWeight, 2nd
2000 - Team Universe Championships - NPC, MiddleWeight, 3rd
again, clearly no suspension
Dave Goodin
2000 - Pro Natural World - WNBF, LightWeight, 1st
2001 - Pro Natural International - WNBF, Overall Winner
2002 - Pro Natural World - WNBF, LightWeight, 3rd
2003 - Pro Natural Masters - WNBF, Winner
2003 - Pro Natural World - WNBF, LightWeight, 3rd
2004 - Pro Natural World - WNBF, LightWeight, 4th
2005 - Pro Natural Masters - WNBF, Winner
2005 - Pro Natural World - WNBF, LightWeight, 2nd
2006 - Pro Classic - IFPA, 2nd
2006 - Pro Natural US Cup - WNBF, LightWeight, 1st
2006 - Pro Natural Universe - WNBF, LightWeight, 1st
2007 - Team Universe Championships - NPC, WelterWeight, 2nd
seven years competing as a pro, then entering Team Universe
Competing for Cars and cash prizes in a different federation is CLEARLY a problem for any amateur that plans on competing in the NPC in the future, and it could jeopardize their amateur atatus.
what about the NPC Hawaii event that gave the winners prizes?