[riverkid]

Both,

1. "If he is such a good doctor"

AND

2. "If he was such a good doctor"

are possible. The first, using 'is' is more confrontative. In English, past tense forms are often used to show greater doubt [more deference/greater politeness]. The subjunctive form and its partner 'was' both do this.

Number 1 could be viewed in this fashion;

A: He's a great doctor.

B: Yeah right! What a quack! If he's such a good doctor, ... .