As Methyl states, UKash is a perfectly legitimate firm which provides a convenient way of transferring money between people. Just like Western Union (with offices all over the world and in almost every corner shop in many parts of the country) and MoneyGram (in every Post Office), their services are used lawfully by millions of people but, just like those other money transfer services, they can also be used by fraudsters.
Such services should only ever be used when the sender knows and trusts the person he/she is sending money to (such as a parent sending money to a son or daughter who has run short of cash) but the services themselves most definitely are NOT scams.