Yes, we can see them! When Mlem crashes on the TestFlight, you will get an option to share crash logs with us. In some cases this is very useful for us because it shows us the entire traceback of the error, which can help us to reproduce the problem.
If you can reproduce an issue consistently we prefer you submit it via GitHub too if possible. GitHub allows us to keep track of which issues we've resolved or not resolved, we're able to ask follow up questions, and you as the reporter are able to see when we've fixed it. If you mention in the GitHub that you've submitted a crash log (and roughly what time you submitted it at, if the crash log was anonymous) then we can find the relevant crash log which is super helpful for us.
We don't really have a notification system set up for TestFlight feedback. I go through it whenever I remember to, but I frequently forget ๐ A lot of people submitted similar crash reports to the one you submitted feedback on, but that particular issue is difficult to reproduce consistently so make take some time to fix.