Employer contributions to 401k affect reciept of SSDI

Our son has disabilities and currently receives SSDI. He started working part time a couple years ago. Now the employer wants to fund 401k for him. He's being told if they do, that is an asset and would affect his SSDI status. He also lives in subsidized housing. Case worker said this could affect his SSDI status and also get him removed from the subsidized housing. Is this possible? He can't touch this money until late 60's and he's 29.