Yes it's ok to use in a 6.7L as far as it is an API CJ-4 oil....that's all it needs isn't it?
This is from their web page.
Mobil Delvac Elite 222 0W-30 is recommended by Imperial Oil for use in applications requiring:
API CJ-4, CI-4 PLUS, CI-4, CH-4
API SM, SL, SJ, SH
CUMMINS CES 20081, 20076...