4ed is constantly stingy with action budget (i.e. most summons require you to use your actions to power their attacks) so I've not seen any rules about being able to create undead that fight along side of you, at least for PCs. They could potentially be very unbalancing for a player character. However, with a little reflavoring, you could make a wizard into a pretty cool necromancer along with many summoned creatures. For example, who says a flaming sphere can't be a flaming skeleton? Rule wise it will work the same, but with the right flavor... Then build a summoning focused wizard and you have a nice necromancer.
I can't say I thought of all this myself, but I recently read the following forum entry which gave me some of the ideas. He fleshing out the reskinning to a greater extent so do check it out about eight posts down in the thread:
Example of a Summoner Wizard Reskinned as a Necromancer