Hmmm, tried this today and following mods do not register their item id's with forge:
Balkon's Weapon Mod
Greg's Lighting updated to version 1.8.4
Regarding Balkon's Weapon Mod, the version included in this package is registered for Minecraft 1.6.2, don't know if this is causing the problem.
Both server and clients throw out Item id missing errors on forge, be it in SSP on a client or in the serverlogs on SMP.
Server still starts quietly , but those 2 mods are not accessible, in Single Player one gets the known error message about the missing item id's, but it's still possible to start a map and play, but again without those 2 mods.
Can't post the error logs right now, could do if requested later this evening, but there's no error from the mod itself, log shows it starts normally, there's only the known forge error about missing id's.
Tested on 2 different servers and 4 different client machines, servers running on Linux and clients all on Windows 7.
Edit:
Seems like logs are not needed, fixed the Greg Lightning problem and:
Balkon's Weapon Mod 1.13 and above are for MC 1.6.2. I installed V 1.12 (latest for 1.5.2) and it works perfectly normal now, maybe revert to that 1.12 version?