Alert Suppression during specific times for specific Nodes

For q1 - Yes, it is probably best to create 2 alerts if you have a set of servers that you always want to be alerted on, and another set where you need to add time supperssion. Advanced Alert Manager has a tab where you can specify the times and days the alert is active. I would use the groups feature to make the 2 sets of servers.

For q2, no we don't have that type of tool.

For q1 you could also use the Unmanage Utility included under the Advanced section in All Programs > SolarWinds Orion to schedule an unmanaged period of time for those nodes. That way your alert could affect every node in your environment evenly.

Your decision to create multiple alerts covering different periods or to use the Unmanage Utility should be based on whether you can live without availability stats.  While unmanaged, you won't know if nodes are up or down.  You won't be able to come in and see what went down last night (at least from the perspective of Orion).  If that is unacceptable, you probably want multiple alerts instead.