CSS values are parsed into tokens by following https://www.w3.org/TR/css-syntax-3/. It looks like esbuild is parsing U+0e2e-0e2f into an <ident-token> with a value U and a <dimension-token> with a value of +0e2 and a unit of e-0e2f. As far as I can tell, this is the correct way to parse this input.
The problem you describe is happening because esbuild is taking steps to prevent a dimension unit that looks like an exponent from being "absorbed" into the dimension value. But in this case this can't happen because there is already an e exponent indicator present in the dimension value, so the parser won't try to consume the unit as an exponent. I think perhaps the correct fix here could be to have esbuild avoid escaping the e if there's already an e present like this.