Hydrolyzes 3-hydroxyisobutyryl-CoA (HIBYL-CoA), a saline catabolite. Has high activity toward isobutyryl-CoA. Could be an isobutyryl-CoA dehydrogenase that functions in valine catabolism. Also hydrolyzes 3-hydroxypropanoyl-CoA (By similarity). 3-hydroxy-2-methylpropanoyl-CoA + H2O = 3-hydroxy-2-methylpropanoate + CoA + H(+) Amino-acid degradation; L-valine degradation. Belongs to the enoyl-CoA hydratase/isomerase family.