“Can 8i Databases be managed with EM10g Grid Control?”
The answer is definitely yes. Oracle have published a white paper to that respect.
Managing Oracle 8i and Oracle 9i databases with Oracle Enterprise Manaqer
10g Grid Control
The only caveat is that the OS must be certified for the 10g Grid Control agent.
As per Metalink Note: 412431.1 Oracle Enterprise Manager 10g Grid Control Certification Checker, Open-VMS or VMS is NOT supported. Therefore the main issue is not the 8i version but the OS. Only the following are supported:
Linux x64 (AMD64/EM64T)
Solaris SPARC (64-BIT)
HP-UX PA-RISC (64-BIT)
AIX 5L (64-BIT)
In any case, Oracle does not support the 8i database anymore except if you have an extended support licence. It may be time for you to move from OpenVMS to Oracle Enterprise Linux (free distribution, lower support cost) from Oracle and have one point of support for both the Oracle OS and the Oracle database. Also upgrade the database at the same time to 11g.