If application needs opened port X UDP, or X TCP combination. Is there any potential risk by opening both UDP/TCP as I usually am not sure which one the application uses?
So, SSH needs port 22/tcp. You're asking if opening 22/tcp and 22/udp presents a security vulnerability. The answer is "no" if nothing is listening to 22/udp. If some other application is listening to 22/udp, an application which you wouldn't want open to other hosts, then it could. There are such combinations (syslog and rsh share 514, for example).
That being said, there's really not much excuse for not knowing which an application uses. On Linux, for example, you can use "netstat -tunlp" or "lsof -i" to see which program is listening to which port(s), and tune your firewall rules correctly.