Yes, you can have up to two affiliate links in a hub, provided that the products you are linking to are related to the hub you are talking about and they are not 'overly promotional'.
In general, a good rule of thumb would be one link per thousand words.
In addition to affiliate links (Commission Junction etc.) you can also post Amazon and Ebay affiliate links from specilised hub capsules.
One point to bear in mind, HubPages does *not* allow Clickbank affiliate links.