It's not unheard of for some of the less focused characters to be successful with a different weapon type. Diala for example is very happy wielding a gun alongside her staff if Gaarkhan is on the team and she just focuses on her support abilities.
MHD has a few abilities that seem complimentary to a melee user, namely improper procedure, fuel injection, field surgeon and combat override. Improper procedure especially seems tailor made for a melee user.
Could a melee MHD be viable in a team lacking a dedicated melee user?