Does having more engineers speed up SPARK repairs?

In the XCOM 2: Shen's Last Gift DLC, you get new mech units called "Sparks", which are repaired with engineers instead of healing like normal soldiers.

Does having more engineers speed up how fast a spark unit is repaired?

From a post here, SPARK units are healed the same way as regular soldiers, but they can only be repaired one at a time, which requires them to be put in the Engineering Bay. Staffing your Engineering Bay with an Engineer will boost their Repair Rate the same way as staffing an Advanced Warfare Center boosts the recovery rate of human soldiers.

It automatically staffs the first SPARK that needs healing (and any subsequent one if the slot if free) you DO still need to staff them in the engineering bay. You can only staff one at a time, though you can send them on missions even if they are not fully repaired.

...but beyond being healed they don't do anything in the engineering bay, it works just like a AWC with how it heals them

Thus, having a bunch of Engineers won't speed up their repairs, but assigning an Engineer to oversee their repairs will. (But you only need one for this)