Hello,
as far as I know the SDK at this time doesn't support subscriptions as they are used within the Orion.This is currently possible only via the SWQL studio connected via certificate, but the SDK API libraries aren't yet ready for implementation of the users subscribers via API.
In my opinion there could be reused the PubSub part of SolarWinds.SDK.Swis.Contract.dll, but this is really not something supported and tested since it's customized for SWQL studio usage.
The easiest and supported way is to query directly against the Orion.AlertStatus entity.
Second possible solution is to use the alert actions like "Execute an external program / VB Script" or "Get or Post" alert actions to contact your event management system or to write into it's database.
I hope this helped to make things a bit more clear.
Honza