Can I use Savable Data Pages to save related Pega data in BLOB tables?

Yes. Even if the class of concrete data is different from the class of the Data Page, it even can be done without an Activity using the "Database save" Save type with:

• A Response Data Transform to map the Data Page data to an instance of the concrete data type; and 
• An optional Validate rule to assure the concrete data instance meets validation rules.

Once upon a time, this needed Activities calling Obj-Save either part of, or called by Post Processing Activities.  Now this can be accomplished with a Data Page using "Database save" and can be dropped into Flows from App Studio.

Zero activities!

Discussion on this topic was sought from the LSA Data Excellence (Pega 8.4) webinar conducted in July 2020. The webinar and its full set of discussions that arose from it are available at LSA Data Excellence: Webinar, Questions & Answers.