That's not a simple question. Of course electric vehicles can work... they've been built for over a century. Of course do-it-yourself conversions can work, just as homebuilt gas-engined conversions of vehicles can work.
The complication is that there are many people, with many different levels of knowledge, skill, and resources, and they make many different plans... some of which are unworkable from the beginning.
As a general trend, if it is in a YouTube video it doesn't likely have any value. Lots of people build things and don't make videos, or don't post them to YouTube. Lots of people like being in YouTube videos, but haven't built anything of value.
The VW Bus was still a work in progress a few weeks ago... and it hasn't been a Nissan Leaf project since the early preparation stage. There are many vehicles described in this forum which are driving around, although those using salvaged production EV motors of any brand are in the very small minority, because those are complex projects that have only recently become reasonably viable; I'm not surprised that none of the Leaf projects being reported in this forum are done yet.
Lots of different things work; none are easy. A motor controller is just one piece of the puzzle. If you want an EV quickly, at a predictable cost, with usable performance, then I suggest buying a used one.
A DIY project intended to more cheaply produce an equivalent to a production EV is as doomed as a DIY project to make a gas-engined car as good as production models in your backyard garage. The projects which make sense to me are those intended to create something that you can't just buy, which typically means a different style of vehicle than is in production; for example, a lightweight sports car or a truck. Among Leaf projects, that could mean different packaging of components (and there are a lot of components in a modern EV, despite the EV enthusiast propaganda), integrating a Leaf motor with a different transmission (which is not trivial), or modifying for more power (which starts a rolling snowball of consequences to other components); in any case, it's unlikely to be straightforward.