My first question would be 'do we ever use 'on' au lieu 'in'? Is it acceptable?
My first question would be, do we ever use 'on' in lieu of 'in'? Is it acceptable?
Yes. "We need to have a head start on the the competition."
Just Google "on the competition" for more examples.
Should we use 'on' like in this phrase:
"All the contestants on X-factor"
Is there a rule?
It isn't so much a 'rule' as one of the meanings of the word 'on':
"as a member of, part of, and engaged in the activities of"