IS SharePoint 2007 compatible with SQL 2008 SP3? I didnt find any know issues with this combination and or a support document which says it is compatible.
Yes, SharePoint 2007 is compatible with SQL Server 2008 Service Pack 3.
As your link covered the "Supported Combinations of SharePoint and Reporting Services Components", I'm assuming you are after these features. So, for the Reporting Services, you need to have this additional Add-in installed: Microsoft SQL Server 2008 SP3 Reporting Services Add-in for Microsoft SharePoint Technologies
Yes, It's compatible. Just make sure you use MOSS SharePoint Service Pack 3, and you should be just fine.
Also there's no difference to SharePoint concern whether you use SP2 or SP3 on the SQL Server. In general SHarePoint installations work with one version up and down of the current minimum requirements. As SharePoint 2007 minimum requirements are SQL Server 2005, all versions of SQL Server 2008 (including R2) works properly.
Reference: MOSS 2007 SP3 with SQL Server 2008 R2