you sure can.. you can add about any liquid into a water bong... most stuff doestn alter the taste butt the only problem with a slushi is that oyu may have to do a good cleaning unless you want your bong to be the color of a blue slushi...
Get a paper towel roll, and insert toothpicks across the bottom of it. Then take Mr. Freezies and place them on top of the toothpicks. Presto, drip free ice toker! Just put the freezies back in the freezer when done and re use them!
The blue bong really isnt an issue, i dont have a proper water pipe anyways, i have a bowl and hose i keep in a glasses case( it smells when u open it so chuck it after a while) And i just buy a bottle of coke and i can make a bong in like 2 seconds so since i chuck it, the blue isnt an issue only my tongue cuz im gunna be drinkin alot of slushie in the days to come