The problem with installing a Jumbo prior to running the FTW is indeed that the machine role wasn't determined yet. Once the machine role is set, some RPMs are being installed by the FTW. Therefore, there is a risk that once FTW is executed after the Jumbo installation, files with fixes can be overwritten by older files that came with the vanilla version.
I'd say that if their system is fine, and if a newer Jumbo was installed successfully since, this can be ignored. But I would recommend installing a newer Jumbo after the execution of the FTW, to make sure the latest versions of all files is indeed deployed on the machine.
BTW - there is a chance that the installation of the newer Jumbo would fail. If it didn't/doesn't, I'd say this issue can be considered as a non issue, and future Jumbos would be installed successfully.