Simple answer : Yes.
Complex answer : No

There are are some basic differences in MeeGo & MeeGo Harmattan
For example MeeGo is using RPM package & Harmattan is using DEB package.Harmattan's API is slightly different from MeeGo because Nokia has added few API's (probably due to swipe gesture)
Google for MeeGo & MeeGo Harmattan differences.Previously I already wrote the basic differences between these 2.

Although there are differences between these two stuff like programs are compatible with both the OS because Harmattan API do support MeeGo API.Plus both the OS are QT based so porting apps is relatively easy.Developers can use Community OBS to drop the codes & produce RPM & DEB packages.There are methods to bridge other differences between these OS.
There are also a team trying to port complete MeeGo 1.2 to N9.Let's see where that goes

IMHO if Nokia decides to continue using MeeGo for other handsets (chances are 0.000000001%) I believe the handset still can be success.Because MeeGo still have part of Maemo/Harmattan "power" & widely accepted Nokia's proprietary swipe UI.
But we all know Nokia went with WP7.Good luck with that...

There are some manufacturer like LG & ZTE expressing their interest to develop MeeGo based handset but I don't know whether it will materialize or not.If they do intent to manufacturer MeeGo device I think they need to somehow acquire the swipe UI from Nokia. Seems like MeeGo is synonym with swipe gesture nowdays.