No, foolishly they haven't included the build folder in the repo. If they had, you would be able to use it without a build step like many other Vue components.
What's worse is that the actual code comes from a REACT component, not a Vue one at all.
Yes, it isn't hard in most cases. You are writing front-end code - remember that uibuilder doesn't actually care whether you use a library or not. The uibuilderfe library just makes sure that you get a link to/from the uibuilder Node in Node-RED. It also provides a simple event system to make sending and receiving msgs easy.
If you look at the vue-apexcharts example in the WIKI, you will see that it pulls in the Apex Charts library and then a wrapper library which just makes things easier to do in Vue.
Looks like eCharts might have a decently flexible gauge. You can set min/max values and min/max angles as well.
There is a Vue wrapper for it with instructions in the WIKI. https://github.com/TotallyInformation/node-red-contrib-uibuilder/wiki/Integrating-ApexCharts-with-VueJS
Google charts gauge also supports max/min https://developers.google.com/chart/interactive/docs/gallery/gauge
You can use that via ChartKick