Can the wife who is a home health care aid, be hired for home care for the disable veteran spouse and get paid?

It depends. Some VA Medical Centers now offers the Veteran Directed Home and Community Based service option. Family members, including the spouse can be hired to provide care. Check out this link and with your VA medical center to see if they offer. Not all do.
http://www.va.gov/geriatrics/guide/longtermcare/Veteran-Directed_Care.asp

No. Wives are expected to care pro bono.