Yes, you need to set option cifs.guest_account and ensure that this Unix user maps to some Windows user which should be considered guest.
simsim> options cifs.guest_account nobody
simsim> cifs sessions
Server Registers as 'SIMSIM' in workgroup 'WORKGROUP'
Root volume language is not set. Use vol lang.
Using Local Users authentication
PC IP(PC Name) (user) #shares #files
192.168.233.1() (DOMAIN\user - nobody[guest])