Common Instance - Combining ASCP and Oracle Configurator Developer in common instance

Hi All,
We have 3 Oracle instances planned for Oracle Mfg implementation (R12) for our client:
- Instance T for transactions
- Instance C for Oracle Configurator Developer (OCD)
- Instance A for ASCP (Planning)

Now the client has come back asking if we can combine OCD and ASCP and have a common instance say:
- Instance T for transactions
- Instance CA for OCD and ASCP (combined)

This will save them cost and be easy to maintain two instances Vs three. Has someone come across this kind of requirement. Can someone share the pros/cons of having this kind of instance configuration?

Thanks,
Nitin jain