Is Blue Iris able to take advantage of the Dahua TiOC features, For example flash the red and blue led's or play a sound file or play one of the build in sound files via blue iris

I was thinking of using the Dahua DH-IPC-HDW3849HP-AS-PV-0280B.

Any feed back would be appreciated.

I don't think so, but you would be best to ask Support in case it has been added.

Even if not directly, I would think there would be a way to run some scripts on events to make that happen.

I'm also interested if these features (Hikvision / Dahua native ones - tripwire / line crossing / person/pet/car/bus/etc / fast moving / crowd/hot spot detection) are supported by BI, because considering switching from a normal NVR to BI.

I'll be recording ~30 "normal" cameras that don't need anything special, just record the stream(s), but also 10 perimeter cameras (mostly Dahua "active deterrence" ones, and a few interior with crowd/hot spot/fast moving triggers).
For the perimeter I've configured tripwire/zone intrusion triggers on the cameras in order to trigger the dual-flashing and siren on the cameras, but I'd like to be able to get an alert when something triggers on these cameras using the native triggers.
Also, on some occasions I'd like to be able to trigger an external alarm system zone - is there hardware that could be connected to BI's PC so simulate an open/close switch?

Is this working in BI ?

Does support answer in the forums, or do I have to contact them somewhere directly ?

Does support answer in the forums, or do I have to contact them somewhere directly ?

This is mainly a user to user forum, so you are best to send an email to Blue Iris Support <support@blueirissoftware.com>

Make sure you add your BI5 licence details, else the email may end up in their spam folder.