ok, i should have held off, if you install the key and apt source, run apt update and apt install ossec-hids-[agent|server], then there is no prompt.
caveats:
1) Run debconf-set-selection first properly for the manage and agent
2) becareful of spacing, it does not seem like they are properly trimmed as there are spaces in the xml tags, i.e. <server-ip> 1.1.1.5</server-ip>. will occur if you have a `debconf-set-selections <<< "ossec-hids-agent ossec-hids-agent/server-ip string 1.1.1.5"` (note two spaces between string and IP)
-- Client --
I still have to get this into a salt state, but i'm running the following:
source /etc/lsb-release
sudo apt update
sudo debconf-set-selections <<< "ossec-hids-agent ossec-hids-agent/server-ip string {{your server}}"
sudo apt install -y ossec-hids-agent
Hope this helps someone else