R5Reloaded supports season 2.1-5 (Season 6 has collision changes on rmdl) all asset types. For models they need to be exported with legion/RSX as RMDL format.
rmdl: Respawn's mdl format, you can export and port from s2-s3-s4-s5-s6, or make one yourself with crowbar, blender source tools or export the models as smd with legion and use crowbar to convert them to mdl format. Then rexx's converter does the rest of it.
uimg: This is used for ui images, minimaps and loadscreens, check my jsons to see more details.
Asset order in a json: dtbl > txtr > matl > aseq > arig > rmdl > uimg
Some extra information regarding season 3 apex assets.
"$type": "matl", #Asset Type, in this case matl which is material
"path": "test/test_material", #Material path, this path is used by world or models
"type": "wldp", #Material type, "WLDC, WLDP, WLDU": Used by world materials, "RGDC, RGDP, RGDU": Used by Static Models, "SKNC, SSKNP, SKNU": Used by nonStatic Models,
"cpu": "texture/blinn_maya_test/blinn_maya_test", #CPU Path, required for material to work properly, can be exported using RSX or LegionPlus. It controls characteristic material features like emissive strengt, fade distance etc.
"blendStates": "F0000000 F0000000 F0000000 F0000000 F0000000 F0000000 F0000000 F0000000", #Required for BM type materials to work properly
"samplers": "001D0300", #Next five entries are flags, controls how material looks (Transparent, wideframe etc).
"flags2": "56000020",
"depthStencilFlags": 23,
"rasterizerFlags": 6,
"unkFlags": 4,
"shaderset": "0x000000000000000", #Shaderset is required for material to render properly, shaderset texture count has to match with Material Textureslotcount or game will likely crash
"width": 32, #Material width and weight, same as first slot texture.
"height": 32,
"textureSlotCount": 6, #Total texture slots being used by this material, has to match with shaderset.
"$type": "rmdl", #Asset Type, in this case rmdl which is model
"path": "mdl/props/kralstest/thisisa_testprop.rmdl", #Model path, game calls the models from this path
"usePhysics": true, #Define if model has PHY. file
"static": true, #Define if model is a static prop, models with only one bone are static props
"animrigs": ["animrig/props/prowler_hatch_tt/prowler_hatch_tt.rrig" ], #Animation rig for the model
"materials": [ "models/vistas/desertlands_mu1/iceland_slopeb_mu1_rgdp" ], #Material paths, used for replacing the material. Usually isn't needed
"sequences": [
"animseq/props/prowler_hatch_tt/close.rseq",
"animseq/props/prowler_hatch_tt/close_idle.rseq",
"animseq/props/prowler_hatch_tt/open.rseq",
"animseq/props/prowler_hatch_tt/open_idle.rseq",
"animseq/props/prowler_hatch_tt/prowler_hatch_tt/prop_bloodhoundTT_hatch_spawn.rseq" #Animation sequences, if animations don't have any rig, they can be added to model this way