General Thank you Template
It appears that there is no current want to generate a letter to a donor advisor (when a gift is received from a Schwab type organization on behalf of a donor). Is it possible to develop a new type of template that would incorporate just about any field, including donor and donor advisor information that could be used for a general (or grant recommendation) type of letter.
Once a donor advisor is added to the donation record, the "tax receipt" switches to recognize the donor advisor as the donor. You can create a tax receipt template for this situation and add it to the donation record so that it prints correctly. If you need help with this, please contact support.