Yes, you can definitely make use of that older material.
I have run a short 4th edition D&D campaign in the Wilderlands and have another ongoing, currently dormant campaign.
Campaign Information and Maps
Using the old background material is great! It allows you to offload the heavy lifting of campaign building. Playing D&D in a settled campaign world that is not the Forgotten Realms, Eberron or Greyhawk is very liberating for the players as they won't come in with pre-set expectations. For example, my players hadn't heard of the Wilderlands before so it was very easy to change or adapt whatever I wanted without being questioned by the players. That which is old is truly new again!
You will have to do some work on the encounters. Fourth edition D&D is a whole different beast than AD&D. For example, the Monster Manual has one fully statted orc with notes on a couple higher level leader types. I see 75 different Orcs via DDI currently in 4th edition! Even if you restrict yourself to the 4th edition Monster Manual there are 7 orcs.
This might seem a bit daunting, but this is a good thing! One of the attractions of 4th edition D&D is the exciting encounters. The Dungeon Master's guide gives some good advice on how to construct good encounters that you should become familiar with.
In general it is a good idea to normalize the number of monsters in an encounter. You may have to work with encounters as a group to accomplish this. Whereas an area might have 50 orcs spread throughout 12 rooms in a small dungeon
- 6 at the entrance
- 12 out patrolling or wandering monsters
- 1 cook with 8 females
- a leader with 3 guards
- 20 others sleeping or milling around in common areas
A 4th edition orc dungeon might have just 3 encounters
- Entrance (with surrounding rooms)
- 4 Orc Drudges (minions)
- 2 Orc Raiders (Skirmisher)
- 2 Orc Berserker (Brute)
- Common Areas (Kitchen/Dining Hall/Barracks)
- 12 Orc Drudges (minion)
- 1 Orc Eye of Gruumsh (Controller/leader)
- 1 Orc Bloodrager (elite brute)
- Leaders chambers
- Orc Chieftain (elite brute/leader)
= Bear (brute)
- Orc Darkblade (Lurker)
- 2 Orc Reavers (skirmisher)
It is pretty easy to level a monster up or down by a couple levels using the directions in the Dungeon Masters Guide to get the exact level of difficulty that you want for an encounter.