You can; I use Great White in everything I grow, not just my marijuana. I dust the roots when I transfer seedlings or small plants from nurseries to a larger container, and mix a dash into my water with biological inoculate for periodic feedings.
It should be fine to use with Fox Farm Trio, or any other organic/non-salt based feed. It's a fungus that forms a symbiotic relationship with the roots, helping them to absorb nutrients from the soil and encouraging and protecting root growth. Just a tip though: make sure you use distilled or Reverse Osmosis water, or let tap water sit uncovered and/or bubbled for 24 hours before using. The trace chlorine in tap water that's used to sanitize it will kill soil life, including this fungus. Letting it sit for a day or bubbling it with an airstone will ensure that all the chlorine will evaporate out, making the water safe for microbial and fungal soil life.