Can I safely disable WinHttpAutoProxySvc if I don't have a proxy?

This service starts and stops as needed so there shouldn't be any reason in particular to disable it.

That said, if you don't have a proxy, there's no need for it. There are no dependencies on this service by other services.

Do not disable this service in Win8/Server 2012 and newer. Disabling WinHttpAutoProxySvc can cause a cascade of stuck threads that depletes threadpools and eventually causes a server hang. I work at Microsoft and have debugged this issue many times.