Can tamper-resistant blocks be removed by an op?

Solution 1:

Sorted this by going into creative mode and removing the block from there!

Solution 2:

According to the IndustrialCraft wiki:

After the safe is bound only owner and server operators may access or use a wrench to remove it. If you changed your nickname for any reason (starting game in offline mode will change your nick to "Player") you will lose access to the safe.
_{Emphasis mine}

While this is the article for the Personal Safe, one would think that the same mechanics work with the Trade-O-Mat because they are both tamper-resistant blocks.

You could also remove it in creative mode. I have never heard of a tamper-resistant block that could not be removed in Creative mode. You could also MCEdit it out or remove it with a mod such as WorldEdit, but the easiest option would probably to cover it up, perhaps with facades (BuildCraft) or panels (RedPower) so that it still looks nice.