I am not sure if there is a technical limitation (I would need to ask that) but even if you would not be using Veeam there are a few things you need to keep in mind:
1) We are talking about closed logs. Only databases that continuously receive thousands and thousands of changes per minute have closed logs faster then 5 minutes. (You can verify that and see for yourself the timestamps per closed log for your databases.)
2) We are and remain backup. Many of our competitors (not that I want to say we are better or so, I prefer not to talk about the competition but talk from our own strength) have the same "limitation" or in most cases it is even 15 minutes. If you want an RPO of less than 5 minutes, you need to consider other defense mechanisms such as @skrause has proposed (there are others also). Don't forget protection of data is a multi-layered approach
3) Even with SQL log shipping, the advised method is 15 to 30 minutes. They do have a theoretical 1 minute possibility but most will tell you that it is not practical and steal to much resources.
Personally, if you are that concerned about the RPO (and I assume that is a business requirement) I would consider investing into 2 things: Have a decent solution with Veeam and choose a good timing (it does not have to be 5 minutes) in combination with SQL always ON.
But that are my 2 cents