If you move to the next page (page 12 of the PDF document), left column, you'll see directions for the 1098 and similar forms.
It appears that you MAY include other material with the 1098 mailings, including promotional materials, etc. The prohibition only applies to 1099 and similar mailings.
John S. Burnett
Fighting for Compliance since 1976
Bankers' Threads User #8