To my understanding, there are some limitations to mixing SONET line cards with DWDM line cards in the same ONS 15454 chassis. I believe one of the limitations had to do with the line card placement versus a OSC-M and OSC. I can't remember the draw backs of doing the above, but there was some negative.
Are there any more draw backs, limitaitons or gotchas?
Also, generally, the optical engineers I spoke to recommended never mixing the cards and keeping them in seperate chassis.