I've taken my bike on the megabus without disassembling it at all. I've done it 4 times.
Before I took one on a coach, I did ask a few drivers what their policy is, and they all said that they are fine with bikes, as long as you have something to cover it over because of bike chain grease potentially getting onto other people's luggage.
That being said, given the lack of clear guidance on their website, ultimately it's down to the driver. I think generally they would be fine with it as long as there's enough space in the luggage compartment and that the bike is fully covered up. So If you're planning to disassemble the bike and have it boxed up, I think that would be even less of an issue.
