Contrary to common belief Rotatillers are actually very detrimental to soil systems, especially for plants. Anyway, with an old maple, the roots will be very well established and will extgend to below the outmost extension of the leaves known as the drip line.
If you wish to plant under the drip line, you best bet is to try to stir up the soil a bit with a shovel but, even better would be to apply a sheet compost with a top layer of composted manure or just plain top soil. This way, you will not disturb the roots of the maple and the new tree can have a healthy soil to grow in and the new soil will also feed the maple.
Given that you have such a well established tree; I picture it being quite large and envision your new tree succombing to blight of some sort.
Though, all you can do is try.