Engineering Lead at Iterable. Previously co-founder/CTO/advisor at Talentral and ZippyApp. Full-stack software ninja polyglot, programming since I was 11. Alumni of Wubyu Games, Yahoo Sports, Ask.com R&D, Intuit, UC Berkeley, etc.
You already said it: "He isn't interested in salary as much as equity."
If this developer is any bit worth his salt, he is worth the equity. A smaller piece of a bigger pie is far more valuable than a big piece of a small (or worthless) pie.
Profit sharing is a red flag to me that just sounds "Cheap," unless you guys are making tons and tons of profit already.
I don't know where you're based, but In Silicon Valley, a good developer can easily fetch $300-500k (base + bonus + yearly equity). UC Berkeley's average starting salary for NCGs majoring in EECS or Computer Science is $108k.
Salary is something a good developer can easily get; why your startup (possibly unstable) rather than another more established company?
If as the other person said, he walks and you're company is crippled, give him equity.
Happy to chat more.