Use of bolded variables in conference paper
For textbooks and self-published material, it is very good practice to follow a convention such as that proposed by Di Carlo, which is widely accepted as the general convention in mathematics.

However, it sounds like are talking about a submission to a conference to be collated and published as conference proceedings. This would typically have a review and editing process like submissions to any peer-reviewed journal would.  In this case, especially since they don't stipulate any conventions, it matters less because they will likely edit your notation where applicable so that all the submissions to the conference proceedings are consistent in notation and formatting.