If you are bent on using it, it shouldn't be very difficult to source out the correct valve to replace the current valve if it's a yoke valve. If it's a DIN valve it might be even easier.
From what I know it is fairly common for paintballers to convert SCUBA cylinders so that they can fill up their own tanks. If you are going to just use it for dispensing you will not need a dip tube. A dip tube is used to move liquid CO2 from one tank to another, without it you would only be able to move gaseous CO2 from tank to tank.
Hope this helps,
Matt