Vinegar is perfectly okay to use but is messy and smelly and does not solidify. Fumarate creates stable solids. Most people that convert their freebase into salt form do so for 2 main reasons. First being storage/preservation of spice. Its is much easier to store a solid(fumaric) than a liquid(acetic). Second reason is because they plan to use the salted dmt for pharmahuasca. Its very hard to consume dmt-laden vinegar accurately, whereas fumarates can be weighed on a scale and dosed accurately. Also, if one wanted to IV dmt, they would not want to inject vinegar into their veins. I assume it would burn pretty badly. DMT fumarate was also FDA approved for medical studies(someone please reference this, I don' t know the details), whereas dmt acetate was not.

I used to salt with HCl. Lol. Not fun when it splashes on you. I just prefered it cuz a giant gallon of it was only a few bucks and I only needed a couple drops every time.