You are right. Without the engineers, there would be no refinery and no wealth creation.
What of the accountants who work for the oil company? Do they create wealth?
That question required even more thought. (Hey, whatchu tryin' to do, make me think...or make my head hurt? ;^) ) But, back to the question, I don't think accounts are participants in the creation of wealth. Without engineers, the refinery for oil would not exist, so an essential step in the manufacturing process halts the production of products from a raw material. On the other hand, at no point does production cease if accountants are taken out of the equation. Granted, they do provide a service, but that service has no direct bearing on the product at any stage from its raw inception point to its final faze before moving to the consumer. Before the advent of mass production, the only persons who did accounting were the tax collectors of potentates. Did mining/oil drilling, farming, or manufacturing exist before mass production? Yes, though on a far smaller scale, but the only persons who needed to keep track of transactions were the immediate buyer and seller. So, I see wealth creation as being existent prior to the need for accounting and if the former existed without the latter, then those who do accounting are not directly involved in the creation of wealth. You may see things differently, and if you do, please post your reasons as I am open to new concepts.