as a DS916+ owner, that mostly does backups and archives, I can say that Surveillance Station support for dahua cameras is pretty basic at best. and that's me being generous.
I am using to see how things go with some cameras, and I do pester synology support to make it better but I'm not hopeful. I will admit that its kind of what drove me to get some cameras 'since I had this thing already'
I know that it's pretty easy to brick a syno config without really trying . to the OP i'd set everything to stream 1. make that the main stream and disable anything in syno from pulling any sub streams, know that its possible to hit the test button have that work and still have it fail for activation. try setting it to generic dahua as well rather than the specific model.
know that resolution, codec, smart codec ..etc stuff must match otherwise it will fail to activate. hitting load capaiblties can also change the config and break stuff.
I recently purchased a Synology DS718+ but initially to be used only for backups over the network. It's my understanding that Synology supports only two cameras for free then every camera after that you have to pay a one-time $50+ fee. That's ridiculous and really adds up it you're talking about a 10 camera system. It's neither here nor there with regard to your question but thought I'd suggest maybe looking into using
Blue Iris 5 for your camera server s/w.
this is mostly correct. there are , AFAIK, a few models of disk stations that come with only 1 camera license baked in. I don't know if some come with zero.
yes, additional cameras are supposed to require additional camera licenses. which is IMO is cost prohibitive and generally not great for a consumer.
some kinds of cameras (multi lense) might require multiple licenses for "the camera". I've read that if you want it to pull from an NVR as well it's probably like 4 licenses as well. any you can ball park 50 USD a license. which is crazy when you think about running 10-15 cameras and how lacking the product really is beyond what can be had from either something like BI or a NVR from you camera brand of choice.
i've never integrated with the point of sale stuff, axis door controllers ..etc ..etc ..etc know that the feature for pulling edge recordings from cameras if the network is interrupted only works on a few brands of cameras. will not work with dahua or hik last time I checked.
none of the 'supported' dahua cams that syno lists will support sending any kind of event marker from advanced stuff like IVS back to the feed. none of them support three streams, many of the supported cameras don't actually work at all if you select their camera name, rather than just generic onvif or dahua generic. (e.g. my 8232 ultra will always fail when I select that model but works under generic dahua).
I will say that they fixed a few issues with their mobile cam app a while ago, mostly with not having as many issues with h.265 support.
note: they do have some support for h.265, however you can't mix streams from a camera between h.265 for the main and h.264 for the sub or vice versa. which is annoying if you want to send h.264 to most of the mobile devices as the older ones might not have hardware h.265 decoding and thus will eat battery on older mobile devices.
the smart lapse was interesting but not super useful I think compared to more modern event based searching.
by default the surveillance folder with btrfs will do check summing and the like, which is odd since the user manual says to not enable that on the folder being used for camera feeds.
note you can have your cameras output to a network share and have files managed that way as well. i've not tried putting quotas on them and seeing how that plays with dahua cameras and when things get full.
I have not talked with anyone running synology dedicated deep learning nvr thing:
DVA3219 | Synology Inc.
but i am not hopeful given how poorly the rest of the game is with device comparability and feature support.
