Rule 1.1.2 of the ICEB publication, "Unified English Braille, Guidelines for Technical Material", available from http://www.iceb.org says:
"For each work, a decision must be made on the spacing of operation signs (such as plus and minus) and comparison signs (such as equals and less than). When presenting braille mathematics to younger children, include spaces before and after operation signs and before and after comparison signs. For older students who are tackling longer algebraic expressions there needs to be a balance between clarity and compactness. A good approach is to have the operation signs unspaced on both sides but still include a space before and after comparison signs. This is the approach used in most of the examples in this document."
By default, DBT will not add these spaces, but there is a way of changing your DBT 11.2 SR2 to automatically add spaces during file import:
Before we continue, may we stress the importance of making copies of the two files referred to below. If you do not, you could potentially damage your DBT installation, and require to re-install it.
Program Files (x86)(64 bit system).
Duxbury Systems\DBT 11.2
Imp-docx.txt(for .docx imports)
Imp-mavis.txt(for LaTeX imports)
| optional: amspco.sbtand remove the vertical bar and space at the start of this line.