Nope. Only 121 SIC time and certain 135 PIC and 91 PIC where an ATP is required. Basically you need to have 1000 hours in operations that require an ATP before you can be a Part 121 PIC. Realistically, that means that any Part 121 Captain has to have at least 2500 hours (or slightly less if they have an aviation degree or military service). They need to get an ATP first, then fly 1000 hours in operations which require an ATP, and then they can be a part 121 Captain.

Assuming they get this 135 operation running, the only path forward for someone who doesn't have ATP minimums would be to be a 135 SIC until getting the hours, then getting their ATP and flying as a 121 SIC for another 1000 hours. I don't think GL is going to be able to hold onto pilots that long in this environment, not unless they pay a lot more. Furthermore, getting the ATP is going to become more expensive due to the ACQ ATP program.