In case anyone else wonders about this, I contacted Ott-Lite's customer service. After about 6 emails back and forth, I finally got the answer to a simple question. She says if the lamp is still under warranty, no, the bulbs are not interchangable. However, if it is not under warranty, do whatever I feel like.
So, not really a helpful answer, but I suppose it answers my question. They don't carry this model at any of the local craft shops, and he refuses to order anything online.