Ok, I found working workaround.
- Create Material that use Runtime Virtual Texture Sample Param
- Create blueprint Material_Instance for this material
- Instead using Material - use Material_Instance as interface source
/Game/land/RVTHeightReader_Inst points to blueprint material instance in game assets
UMaterialInterface* Material = LoadObject<UMaterialInterface>(nullptr, TEXT("/Game/land/RVTHeightReader_Inst"));
UMaterialInstanceDynamic* DynMat = UMaterialInstanceDynamic::Create(Material, nullptr);
- right now setting RVT works:
DynMat->SetRuntimeVirtualTextureParameterValue("RVTRead", RVT);