If you're concerned about using good practice, you really shouldn't rack fresh wort onto a used yeast cake. The trub contains a lot more than just healthy yeast, and doing this doesn't allow you to control your pitch rate. I know that doesn't really answer the question, but it seems that your general procedure leaves more room for error than the oxygen factor.
Downvote all you want, but I quote:
A number of homebrewers have adopted the practice of transferring the beer from a fermentor and the end of fermentation and then adding a new batch of wort on top of the yeast cake. This is a bad practice. Can this practice make good beer? Absolutely. Will it make the best beer possible? Absolutely not. The yeast at the end of fermentation is not just healthy yeast. There are plenty of dead cells present, as well as the break material and hop bits from the previous wort. You must collect the yeast, look at the population, remove dead cells and nonyeast material by rinsing, and then reuse only the proper quantity of cells in the next batch. Do not be lazy. Always clean and sanitize your fermentor between batches, and always ensure you are pitching the correct number for cells for the beer you are brewing. Yeast growth is important to beer flavor, and overpitching (especially with excessive trub) can have a negative effect.
Source: White, C. and Zainasheff, J. Yeast: The Practical Guide to Beer Fermentation. p 164.
So yes, reusing yeast is fine, but racking fresh wort onto old yeast is not fine. Not that you can't do it, just that it's sloppy. If you're gonna do it, though, might as well not bother with aeration.