A large thigh abscess develops at the surgical site after a femoral artery embolectomy, is incision and drainage the only treatment required?

Yes. An abscess, or collection of infected fluid should absolutely be drained. If left undrained, it could compromise healing if the opening in the artery, and the suture line could blow out leading to a high risk of death. Call your surgeon immediately! an infection of the skin without and abscess is best treated with antibiotics.
Possibly. If no graft or foreign body was included at operation, then adequate drainage may resolve the issue. I suspect most would use antibiotic as well, and culture the drainage to pick the best ones.

Related Questions

An abscess develops after a femoral artery embolectomy. Incision and drainage is done. How long should it drain before debridement?

Already occurring. If a drainage procedure was done the wound should have been left partially open. The dressing changes will do the debridement. Make sure to change daily. Follow-up with surgeon who did drainage procedure. Read more...
Until it is done! The abscess must drain until all signs of infection are gone, but you can still undergo a debridement in an infected field -- often this helps clean out the infection. Read more...