I'd think that if the Spurs, Suns, and Heat end up with the same record, the tiebreaker procedure would follow the "more than 2 teams tied" procedure, only you would subs ute breaking the tie in the conference for breaking the tie in the division. So, you'd get something like this:
1. break the tie in the conference. San Antonio would own the first tiebreaker over Phoenix. The only remaining tie is SA/MIA.
2. head-to-head tiebreakers:
a. games against each other -- SA 1, MIA 1
b. winning percentage within own conference: Heat are 34-6 against the East; Spurs are 27-11 against the West. That would give the tiebreaker to Miami.
Given that scenario, if you wanted to root for particular results, I think the Spurs would want as many Heat losses against the East as possible. But it seems implausible to me that that Miami will lose 5 more games against East teams than the Spurs will lose against West teams.
Basically, if the Spurs and Heat end up tied, the Heat will own the tiebreaker.