Sorry, I did not have any data about x670-G2 <--> HPEQSFP+ Active Optical Cable at now. But, I known that one customer was using HPE FlexNetwork X240 40G QSFP+ 3m Direct Attach Copper Cable to connect X770.
Based on x670-G2 datasheet, we support QSFP+ Active Optical Cable. However, we cannot warranty the 3rd party cables will be works well !
If you verify connection x670-G2 <--> HPEQSFP+ Active Optical Cable, kindly request you could post your result on this post.