Can I use the Nexus repository manager with the IDE?
Yes. Just set up Nexus as described in its documentation, including changes to your settings.xml as in Guide to Mirror Settings, and the IDE should work correctly with it for purposes of resolving artifacts.
One point to note is that as of NB 7.0 the IDE will honor your mirror settings for downloading remote repository indices, but this cannot work for Nexus groups if you have individual repositories configured in the IDE. Since 7.0 ships with three remote repositories enabled (7.1 displays just those remote repositories used by open projects), and you would expect indices in e.g. Maven Repository Browser to reflect only artifacts actually hosted on those public repositories, you should configure your mirrors to go directly to Nexus's proxy repository rather than the public group; NetBeans will refuse to download an index from a * mirror.
For most projects it should suffice to list:
<mirrors> <mirror> <id>central</id> <mirrorOf>central,java.net,java.net2</mirrorOf> <url>.../nexus/content/repositories/central/</url> </mirror> </mirrors>
(Note that the java.net repository has been merged into Central so any old repository definitions for it can simply be redirected now.)
If you do NBM development, in which case some projects declare a repository with the ID netbeans pointing to http://bits.netbeans.org/maven2/ then you also want:
<mirror> <id>netbeans</id> <mirrorOf>netbeans</mirrorOf> <url>.../nexus/content/repositories/netbeans/</url> </mirror>
and similarly for any other remote repositories you may require.