The cartridge does support reactions. However, reaction information cannot be stored in compressed OEDBMols. If use_compression is set to true in the configuration file and a reaction is stored in the molecule cache then the reaction will be stored as an OEMiniMol.
To use reactions just use the functions and domain operators as described above. For structures, substitute SMIRKS for SMILES. For specifying substructure queries substitute reaction SMARTS for SMARTS and MDL Rxn blocks for MDL Mol blocks.