Weird is a weird word. What is weird to one may be an absolute necessity to another, and we have not yet seen how this will work out with GC3 (they have not told us as yet).
Weird as in "not how games normally do this on Steam." The standard method would be to release the alpha by giving people a code. When the beta comes, just update the alpha to the beta and hand out more codes. etc. Unless something happens that requires a reinstall (which is possible but unlikely at this point, though being asked to clear user data could certainly happen at any time), there shouldn't be a reason for any special Steam instructions.
That part comes when the game is released and they want to do a beta of a patch or some such. For that, people have to opt into the beta branch for the game or they won't get that beta patch. During alpha/beta itself the game is that and if you have a code, that's what you get. Easy peasy. 
So you can tell me right now what mechanism they will provide for trapping "loops" and "hangs"?
Of course not, I don't work there. 
I'm just saying that speculating about how this stuff will be done is a total waste of time, becuase it's guesswork. Who knows how they want bugs reported this time?
These are the most difficult types of programming errors there are to diagnose. User descriptions of what they were doing may be useful in some cases, but not all, and can be completely unrelated to the actual cause. The only way to be sure of finding the cause is to capture data from the PC at the time of the event and delivering that data to the programmer responsible for diagnosing the problem. This can't be done without user interaction, which requires a command to activate the process. Does your experience with Steamworks give any clue as to how this might be accomplished? My experience with Steamworks is totally lacking in this regard.
Capturing it can be done without user interaction. Debugging & instrumentation tools have come a tremendous distance in the last few years. They might need you to upload a dump in those kind of scenarios, but Steamworks helps with a lot of that (as do more modern development tools, IntelliTrace can do some really remarkable things).
I want these questions in front of the devs so they can ponder their answers when they craft the instructions they give us with the release of the external alpha code. If they already have the answers, excellent. If not, the success of GC3 depends on them hearing these questions before they craft the announcement and instructions for the external alpha release.
Fair enough.