In reply to Blackletter Questions:
Schwabacher and Bâtarde are fairly closely related, within the larger category of blackletter, but are distinct enough to exist as separate sub-categories. This is especially true in manuscript, in which Bâtarde styles tend towards greater informality and faster writing. In type, the similarities may be more obvious, as the Bâtarde will tend to be formalised. To get a feel for the differences, I recommend doing Google image searches on the two terms.
Conventionally, use of blackletter in mathematics had tended to be a fairly light form of fraktur. A Bâtarde along the lines of the Duc de Berry type would be appropriate weight, but I couldn't say whether the letterforms would be readily accepted by mathematicians. Remember, in the context of mathematics, these characters are being used a symbols, not as regular text, so it is important that they correspond sufficiently to expectations.
