Dahua IVS and Hik Smart Events are communicated using PullPointSubscriptio, which requires a few extra clicks in BI to enable.
In BI, check these settings (on the camera you're working with):
Camera properties > Video > Network IP Configure... > click "Get events with PullPointSubscription"
Camera properties > Trigger > Sources > click "Camera's digital input or motion alarm"
If you do that, when an IVS rule triggers on a camera it should cause
Blue Iris to trigger as well.
Just a heads up about one potentially annoying issue you may run into if you get this all setup. At one point, using PullPointSubscriptions with a Dahua camera caused the camera to enable its regular "Motion Detection" feature, which you're probably NOT going to want enabled if you're using IVS (because it'll likely cause a lot of false positives). So if you notice "Motion Detection" being enabled on the camera when you don't want it, one of the easier workarounds is to configure it so that it never detects anything. i.e. make the area it's looking at small and slide the sensitivity bars high so that nothing triggers it.
On my BI system, I have BI do its own motion detection on most of my cameras (i.e. no motion detection/IVS is configured on those cameras). Two of my cameras do an excellent job themselves detecting motion, so I have them setup to detect motion and BI setup with PullPointSubscriptions to look for that. One of those cameras is the 1831C-PIR (which has a built-in PIR sensor) and the other is a Starlight+ model like in this thread (where the AI piece has been doing a great job of triggering only on cars/people).