if we have a credit or debit card information, could we add credit or debit card programmatically into Google Wallet either from Android app or server code?
No, and IMHO, that would be counter to what Wallet Instant Buy, is all about.
Q: Why have Virtual Onetime Card numbers?
Increased security: If the one-time card number is compromised, a fraudulent user can do little or no damage. Google users expect Google to not share their real financial information.
Simplified technical integration: sharing Virtual Onetime Card numbers allows Google to dramatically simplify merchant integration (eliminating complex encryption, dedicated keys, direct connection between Google and merchant's data bunkers, etc.)
You're probably looking for/comparing with other credit card processing gateway/services which do have options for such (e.g. store and "tokenize"). Wallet Instant Buy isn't such - see this FAQ.
Hth...