According to the following, the city of Velva, North
Dakota was named that because of the "velvet-like" appearance of the surrounding countryside:
http://www.webfamilytree.com/North_Dakota_Place_Names/V/velva_(mchenry_county).htm
You can't assume that just because other members of the family had "established names" that they wouldn't have created the name Velva on their own. The huge majority of parents have no interest in etymology or whether or not a name is "established" and choose names based on other factors.
The earliest Velva in US Census Records on Ancestry Library seems to be Velva
Warren, born about 1811 and living in
Georgia in both 1850 and 1860.