Here are some things ive found

Tested with a clean garrysmod

Mode: SP = Singleplayer & MP = Multiplayer
Mods: Nothing
Cheats: Off
Activated contents: CSS, DOD, HL2, HL2 DM, HL2 EP1, HL2 EP2, HL2 LC, TF2

Nr.1: If you spawn a npc with a SS weapon you get this error
[Serious Sam SWEPs] lua/weapons/weapon_ss_base.lua:98: attempt to call method 'GiveAmmo' (a nil value)
1. unknown - lua/weapons/weapon_ss_base.lua:98
2. Spawn - [C]:-1
3. InternalSpawnNPC - gamemodes/sandbox/gamemode/commands.lua:400
4. Spawn_NPC - gamemodes/sandbox/gamemode/commands.lua:433
5. unknown - gamemodes/sandbox/gamemode/commands.lua:463
6. unknown - lua/includes/modules/concommand.lua:54

Nr.2: Make all SS weapons able to use for npcs correctly

Nr.3: Make the killicons for the weapons a bit bigger

Nr.4: The charg sound from the "weapon_ss_grenadelauncher" is missing

Nr.5: May change the animation from weapon "weapon_ss_colt" from the pistol to the revolver one

Nr.6: Make "weapon_ss_grenadelauncher, weapon_ss_cannon, weapon_ss_laser and weapon_ss_ghostbuster" able to destroy NPC Helicopter, gunship and strider

Nr.7: Make "weapon_ss_flamer" able to destroy NPC floor turret

Nr.8: Make "weapon_ss_rocketlauncher" albe to destroy NPC Helicopter and gunship

Thats it so far i hope there will be some changes soon - Combine