Yes, that would work -- assuming the SS 4 modules are
user modules, as most of the third-party ones are. They would just need to use the
User > Import SwordSearcher 4.x User Module menu function in SS 5 and then point it to the location of the module they downloaded and extracted.
Since
Forge is now available, it shouldn't be too long before third-party modules are updated for SS 5. It's been less than a week since SS 5 has been released, so beyond sending them a polite email you should probably give then a little time.