Definitely! This process is a must before you use a poly-cotton tent for the first time. It allows the fibres to swell and knit together at entry points such as stitch holes and seams before going out in the rain.
Pitch the tent on a dry day and spray it with a hose (not too much pressure but so it is wet), especially on the seams. You may notice it leaks at first although this is to be expected. Leave the tent to dry out and this will allow the fabrics to knit together and create more of a water resistance.