Is Netflow enabled on your devices? Can you run a test with host name and community string successfully?
You may want to try adding the device by IP Address rather than DNS name and see if this helps. If not, you might want to hold from looking at that device.
Let us know how it goes-
To my knowledge, there are no plans to make Toolset's Network Performance Monitor tool use a different database backend other than the Access/Jet engine. SolarWinds provides a different product, Orion Network Performance Monitor (http://www.solarwinds.com/products/orion/index.aspx), which allows you to take advantage of SQL Server as your datastore.