Vent stacks must be designed for a fire at the outlet. The mesh is designed to ensure no blockage of the vent stack by animals/insects. 

Additionally, the mesh must be designed for pressure drop to ensure code-compliant back pressure on the relief devices.

No, but it is always necessary to determine the possibility of an adverse chemical reaction with the particular material being used for the mesh.

I am communicating with a company that is exploring this technology for an application involving a mixture of flammable gases, including hydrogen.

The Panel has not received such inquiries. Section 14.2 of NFPA 69 Standard for Explosion Prevention Systems covers foam and mesh requirements. NFPA 69 states in 14.3.4 that the tests shall be conducted with a flammable gas/air mixture with a fundamental burning velocity representative of the burning velocities of flammable vapors expected in the intended applications.