I've been running 25 mm tires on 29er XC rims with 18-19 mm internal rim width for many years so I have given this a lot of consideration (light 700c disc wheels were once impossible to find).
IMO, you really need to contact the manufacturer and ask them the maximum pressure this clincher rim can accommodate. If it's some ultra-light butted scandium rim you might find yourself endoing as the rim explodes and gets caught in your fork.