A consultant is not an employee. As such he is not expected to follow the leave rules, rules relating to hours of work, office timing etc. His fee will be paid as per the bill raised by him. No PF is deducted from it. He is given form 16A and not form 16 in respect of TDS deducted. As such, he is not an employee and not eligible or leave or leave encashment.
However, many IT Companies who believes that labour laws are not applicable to them, engage employees are consultants! They are designated as consultants but are expected to reach the office in time, remain in the office or 8 to 9 hours, follow the dress codes at par with others, avail leaves, report to somebody on daily basis etc. This is an arrangement to avoid paying PF, Bonus and other benefits available under labour laws. When he leaves the organisation after long service he will not be paid gratuity saying that he was not an employee.
If your Consultant falls under the second type, he should be given leave encashment.