In Florida sandy soils we need to get organic matter into the soil. I am wonder if that stuff from the vac. would help in that regard. Cannot decide how much organic might be there. Seems like it would be better to mix into garden soil than to send it to the landfill.
while you would gain some organic material that could compost into the gaden, there would also be a lot of other material that would not be. Carpet fibers, pet hair, things like that, which would not be good for soil amendments. a better option for you, if you have not already done so, would be to look into composting. many vegetative food scraps can combine with yard trimmings to form a good compost medium to add to sandy soil.
It most likely would not hurt but I would think that it would have little or no value for your garden
The vac bag contents will be mostly very fine dirt, grit, etc., and wouldn’t help the sandy soil much; it might even make it worse for holding water or turn it into cement.
The answer to your question is, NO.