In a patient with isolated inguinal nodal recurrence one year after a margin negative anal excision for Grade 1, T1 SCCA of the anus, would you include the anal canal/rectum as part of salvage chemoradiation therapy?  

Absolutely yes- the risk is lower for T1 8-10 percent but it is possible. Given the failure should include the entire anal canal and RNI to at least 45 /25 and can SIB gross node to 50 plus depending on size. Anecdotally I had one case like this , resected small T1, node failure where only the ingui...

Yes. Pelvic and perirectal nodes are at risk.

I agree with @William M. Mendenhall as long as it were anal canal and not confined to the anal margin. There was probably a 5-10% chance of that happening with a T1, but since it did recur in a node, comprehensive nodal coverage is warranted. If it were anal margin, I would leave out the rectum.