Is it possible to add/update asset via rest api in asset management module of SapphireIMS?

Yes, SapphireIMS supports Rest API for creating/updating/searching asset in SapphireIMS system. For more details, please refer "Asset’ section in left side navigation in our online help link https://api.sapphireims.com

Please note that SapphireIMS Asset API use key and token based authentication. For more details, please refer ‘SETUP YOUR ENVIRONMENT’ in the above online help link provided.