** A plumber told me a siphon break is no longer necessary. Is that true? **
A 'siphon break' (usually created by installing an air gap mounted on a nearby sink) was never required by a dishwasher itself in order to function properly but rather were mandated by local plumbing codes.
If your plumber is familiar with local plumbing codes, then he should know. No one here is likely to be able to tell you what your particular locality's codes are without you stating where that is. Check with your local authorities.