There are a lot of things about the "standard-issue" 206 that people don't completely understand. Having the throttle open will not prevent a start attempt (heh, but you better be quick to react !). They will start quite happily with the boost pumps off. Similarly, they'll start right up with the de-ice/anti-ice valve on. They'll start (sort of) with the fuel valve "Off." Heck, they'll even start with the rotor brake on (or alternatively, the main rotor blade securely tied down).
The reality is, as others have pointed out, that the Allison 250-series will absolutely start with the Generator switch in the "ON" position. Yes, as soon as you release the starter button, the generator will start generating. No, it won't effect a thing...in most cases.
Excuse me while I slip into my "grizzled old-timer" mode:
Back in the bad old days...when our 206A's had weak-ass C-18 engines with weak-ass NiCad batteries, the generator load could possibly drag the N1 down below 58% if you turned it on prematurely - like right after start. So we let the starter cool for a minute, then goosed the N1 up to 70% before making it switch over to be a generator. However, with modern batteries and stronger engines, this is simply not a problem.
If you watch most 206 pilots, few release the starter right exactly at 58% anyway. Some keep it depressed right to 62% and nothing bad happens. It's hard to hit that 58% mark, especially if the engine is accellerating rapidly. If that is the case, once it gets over 50% I release the button. Usually it'll be right at 58% or so when the button unclicks. But who cares, it's not *that* important.
Leave the generator switch in the "ON" position all the time and it won't hurt a thing. At least you'll never forget to turn it on. And in a 206B there is no caution light to remind you that you didn't (oops! - raise your hand if you've never done this). However, leaving the generator on all the time is counter to the published checklist, and of course the Decel Check (in the C-20 series) is predicated with the generator off.
In multi-engine aircraft that use the Allison 250 engine, as soon as you start the second engine you can switch it immediately to "Generate" with no delay, no one-minute wait, and not even having to increase the N1 to 70%. This should tell us something.