Blood loss wound effect wound healing in two ways that I can see:

1. Low pressure or low hematocrite will generate hypoxia

2. Transfusion of blood has an immunosuppressive effect as shown in many publications

I do agree with Dr. Michael ER Olausson. Hypoxia can play major role in case of that. But, I am not sure about the extent of wound healing.

The process seems simple enough, but wound healing is actually quite complicated and involves a long series of chemical signals. Certain factors can slow or prevent healing entirely.

One of the most dramatic factors is reduced or inadequate blood supply to the wound. The oxygen and nutrients that new blood carries to the wound are essential to successful healing. A wound that is not getting enough blood could take at least twice as long to heal, if it heals at all. By some estimates, as many as 6.5 million people in the United States suffer with wounds that are not healing well. These are called chronic wounds, which are more common in people with diabetes, high blood pressure, obesity, or other vascular disease.

I fully agree with the previous answerers.

The rheological properties of blood seem to be best for surgical wound healing (as in flap surgery) providing enough O2-carriers and not too many cells at a Hb level of about 10g/dl with a hematocrit of 30%. 

Basically I agree to Dr Olausson. These are the primary effects of blood loss. If you check the available literature on shock, resuscitation, hemodilution and treatment of critical ischemia (hypoxia), you will however find that dilution of the hematocrit down to levels of 24-30% improves microcirculation. As a consequence oxygenation of critically perfused tissues is even improved. For clinical relevance I recommend to check Spahn et al. Critical Care 2013, 17:R76 (recommendation 17 is very interesting regarding you question). 

I agree to the point that low blood pressure will reduce tissue oxygenation, but lowering the hematocrit does not necessarily result to hypoxia. 

Migration and homing of stem cells to the traumatized tissue need circulation. Would be an interesting experimental study to follow stem cells during trauma AND hemorrhage. 

I agree that blood loss by trauma influence in wound repair because wound healing depend on adequate microcirculation to supply nutritients and oxygen.

In a prospective observational study we just found (not yet published) that FXIII levels decrease after trauma to levels around 60% and below. Since FXIII is very important for both, cross linking fibrinogen at the end of the coagulation cascade and wound healing, it seems important, that FXIII should be measured whenever trauma patients have continous bleeding tendencies during the first 8-10 days on ICU, or show wound healing problems. In case of such a clinical Situation I would recommend administration of a FXIII concentrate.