can my client setup own subdomain on raq? or i have do it myself upon their request?

Unless you set a wildcard on the domain and let them use some sort of script, or redirect the subdomain otherwise (headers, etc.) then yes, you have to set it up for them.

does racksack raq4 give wildcard?

Errr, well... that is something you'd set up in your DNS for the domain. I'm not sure how rackshack and you handle DNS.

ok. I will forward on this myself.