@viragomann
Sorry I never replied back with what I found out. It turns out that you can do this but it requires a setting in the OpenVPN client and Outbound NAT settings. I only figured this out through many iterations of trying every possible reasonable setting.
Create a firewall Host alias that contains the domains you want to force through a specific gateway. Enter the domains/URL's there. When you save it will fetch the URL's, so do this first or your list might not be updated with resolved IP's.
Add your firewall "host" alias (that contains the list of fqdn's you wish to force through the specific VPN Gateway) to the "IPv4 Remote Networks" field in the OpenVPN client settings. This is what updates the routing table. Note that the remote networks field does not auto-complete the alias when you type it (unlike most fields), but it'll fail if it's the wrong type or non-existent.
For the outbound NAT settings: set the interface to the VPN you want to force the domains through, IPV4, any protocol, source any, destination -> network or alias - use an alias created in pfblockerng OR the one you use above, [gateway] translation [your vpn client name] Address, and place it at the very top of the Outbound NAT rules
For pfblockerng alias, it can be used for the outbound NAT config but cannot be used for the OpenVPN client config (you can probably ignore pfblockerng and just use the built in URL alias option). In the pfblockerng settings create IPV4 alias and set the domains for Whois with state On and enter the domains. Under settings use Alias Native and pick your update settings (For local alias I'm pretty sure you can just leave it disabled, but it doesn't really matter).
It ended up not working for what I wanted to use it for because the domains in question end up forwarding, but at least there is a way. I did not find this documented anywhere.