Hi Dick
Yes. You can set default revenue account for specific customer group via Advance G/L Determination.
For detailed information, you can refer,
1. "How To Setup and Work with Advanced G/L Account Determination guide" which can be downloaded from SAP Business one customer portal under documentation tab.
2. http://www.youtube.com/watch?v=9BXlaJKHI2Y
Hope helpful.
With regards
Balaji Sampath