Usually minor differences don't matter (like if one device is running version 3.3.8 and another is running 3.3.10), but it's a good idea to try and use the same versions. When there's a major version change (like from 3.3 to 3.4 or from 3.4 to 4.0) then you might miss some functionality until everyone gets up to date. It would be ideal to coordinate those larger upgrades with your bandmates.
Your iPad 1 is limited in what iOS version it can run, but at this point it can still run the latest Set List Maker version, and that's what matters for syncing.
You can find the version of any installed app from the Settings app, in General > Usage > [app name].