Well known to Hill and David Flitcroft from their time at Barnsley, Mellis cut short his contract with Mansfield Town to join the Whites until the end of the season.
An impending court case looms heavily over the 29-year-old, however, which leaves his longer-term future unclear.
In January this year Mellis denied charges of affray, assault and causing grievous bodily harm at Nottingham Crown Court following an incident on a Mansfield street the previous August.
The case is due to be reviewed at Leicester Crown Court in March and a trial set for November 30.
Last August Mellis was fined two weeks’ wages by Mansfield and warned him about his future conduct, later releasing a statement issuing his “unreserved apology.”
Hill says he did not think twice about bringing the player to the University of Bolton Stadium to help in Wanderers’ survival effort, which continues today with a visit to Coventry City – now playing at Birmingham City’s Trillion Trophy Stadium.
Mellis played for the Under-23s on Monday night and the Bolton boss confirmed he had not yet reached match fitness. But Hill is confident the ex-England youth international can be an asset for Wanderers.
“Not every footballer can be a role model,” he told The Bolton News. “We’re a cross-section of people from society, wherever you are brought up or whatever your demons are.
“As a football player he’s very good. He is a good person – but sometimes good people can make mistakes. We have emotional triggers which can stimulate bad reactions in you.
“I have worked with similar characters to Jacob in the past and I will in the future. I have no problems dealing with him as a person or a football player.
“I think he makes us stronger in the next 18 games and after that I don’t know. There is no gamble. Is he better than what we had? Yes.”