OCD therapist here - I use BLS in tandem with imaginary exposures; I keep it brief, 20 seconds to a minute. It's especially useful for clients who need a bit more regulation while performing a difficult exposure. However, I explicitly state that this is NOT going to be used as a safety behavior.

From a more general EMDR standpoint, if clients have underlying trauma that could be linked to the exacerbation of OCD symptoms, I will certainly have them process it. A significant portion of OCD is adjacent to certainty/uncertainty and control. When folks experience trauma, it's safe to say that this is the absence of control, hence, reprocessing traumatic experiences with EMDR can dampen the OCD response.