With the DIRECT pathway you are able (and required) to sit for the ABR exam. The only way you can get a CAQ in Vascular/Interventional is by being board certified in DR first. Diagnostic training is certainly shorter in DIRECT, as a result graduates might not be as comfortable covering the entire breadth of the diagnostic field.
Btw, there is a stand-alone IR residency. It is the 'new' vascular surgery training scheme: 3 years of general surgery, 2 years of IR, 1 year of vascular surgery.