Private IP class

You should be fine using what ever range you wish. Private classes are just that private. These two ip's will be used for the end points of the VPN tunnel so won't interfere with your public stuff. You could even use a random non-private IP address for this purpose but that would interfere with someone with that IP trying to connect to any services on your Linode or vice versa as your Linode would have a route through the VPN for that IP.