Hello, I am currently doing a research on this same topic. Did you end up finalizing yours?
This thread is 10 years old, so you might be lucky to get a response from the OP!
If you're thawing juice that is truly aseptic, then there should be no microbiological risk for ambient thawing. This format should be ambient-stable, with chilled/frozen storage being used for some types of juice, or where a particularly long shelf life is required, as it gives better long-term durability of the organoleptic characteristics that tend to be the limiting factor for shelf life. Nonetheless I'd suggest clarifying with your raw material supplier(s), just to get confirmation that this is the case - sometimes you'll see a note on specifications that short-term ambient storage and handling is fine, but temperature-controlled conditions are recommended for long-term storage.
For non-aseptic juices I know of plenty of sites that thaw at ambient temperatures, but it's not something I'd generally recommend - particularly with lower brix products in larger unit sizes, where the thawing time can be such that the outside can potentially start fermenting before the inside is thawed. Even without the obvious risks that should be apparent with a cursory consideration of the thawing profile, I've seen this go wrong plenty of times, and received a dismayingly large number of complaints to the effect of "we abused the product, it fermented, so we're rejecting it and want you to investigate..."
IMO the only exception where ambient "thawing" might be acceptable is for very high-Brix concentrates (typically those at or above about 65 °Brix), where they will still be liquid at -18°C so it's just a case of allowing the temperature to rise slightly so that the viscosity reduces to a point where your pumps can handle it - you're not "thawing" these products in the sense of needing to achieve a phase-change from a solid to a liquid. As long as you've got half-decent pumps, many of these are entirely useable before they get near 0°C, let alone above it, so a very short spell at ambient temperature can potentially be used without significant risk, as long as it is monitored and controlled.