Yep, it's against the rules! You could find much more primitive and basic pinhole cameras than the ornate things that populate the Zero Image stable.
Framing of the scene is a careful judgement call based a lot on experience (e.g. by making your own pinhole camera out of a tin can or container or whatnot) and a bit of guesstimation.
One should not really consider it absolutely critical to get framing exact, because one of the thrills of pinhole photography is the unpredictability of the finished image -- exposure and framing could one or both be out. For many, many people, it's "big deal", and they're really chuffed to come away with anything (cf. the entries in the Worldwide Pinhole Photography Day website). The Zero Image cameras are more of a flash, polished style that fits a belle epoch of luxury imaging -- most of them certainly are not "primitive" in the true sense. Some LF models have brass dots in the top panel to assist with framing. I think view lines make it too easy for people to frame a scene while others relish the mental exercise in 'fitting' a scene to the format in use without any visual aids (save for the plastic viewfinder 'guide' supplied with Zero Image pinhole cameras, which I used when I first started 8 years ago). Ultrawide angles of view and extreme depth of field (f235 for the 6x9 multiformat with an 0.017mm pinhole) certainly take care of any small errors. As important as framing is the fact that you need a very strong foreground subject that is quite close to the camera, otherwise everything will be way out to the horizon and not provide any viewing impact. I made the image below at Milford Sound (a day after 1.4 metres of rain fell) in New Zealand very quickly as my impatient niece toe-tapped behind me. I thought at the time I had aimed the camera too low and off-centre. I was also close enough to reach out and touch the nearmost part of the wood debris!
• ZeroImage 6x9 multiformat (as 6x6), ACROS 100, multispot/M-WAvg metering).