Technic Pin/Travis Brick Legal Connection?
In general, this sort of connection is illegal, but I think that it works fine with a Travis brick. Technic pins must be "in click" in a model, or the pins will be held in compression and can be damaged over time.

Here's a slide from Jamie Barard's classic "Stressing the Elements" presentation that explain the need to have Technic pins in click:



And here's the slide that explicitly states that Technic pins should not be used to connect to System bricks:



Here's an example of a set that didn't keep Technic pins in click and the resulting damage from prolonged storage assembled:



With all of that said, the four holes that run through the stud connections on the sides of a Travis brick provide ample room for a pin to click into it. This isn't an obvious connection as with a Technic brick, but the fact the pin can move freely inside the brick indicates that it isn't in compression and is simply constrained to remain inside.

I can't speak to whether or not this type of connection would get through a design review today, but I can say with confidence that this wouldn't cause damage to elements. If this is considered "illegal" it would be for other reasons.