I Am Having a Spinal Fusion in March, is It Safe to Have a Tummy Tuck 2 Months Prior?

This is a decision that should be made by the surgeons involved with your care. The issue that worries me about your idea is not the tummy tuck part but the fat transfer. Transferred fat has poor blood supply and injecting into an area near the site for a spinal fusion could increase your risk of infection.  If a spinal fusion gets infected  you will have big trouble. I would follow the advice of your surgeons regarding this idea.

You must absolutely address this question to both your aesthetic surgeon and your spine surgeon.  If the spine surgeon plans an abdominal incision with retroperitoneal approach to your vertebrae, this dissection may (or may not) be affected by abdominoplasty.  If an alternative approach will be necessary as a result, you should know this in advance, and time the spinal and aesthetic procedures accordingly.

The timing of a tummy tuck as regards a planned spinal fusion is a question that you should be asking of your two surgeons. This decision would also be affected by the approach that is planned for the spinal fusion. Theoretically, if everything else is OK, 8 weeks between a tummy tuck and the spinal fusion may be acceptable. However, if there are any untoward issues, this may not allow adequate time. Then there are other issues such as nutritional status, weight changes, etc.