Don’t assume Flash is a useful development tool for a particular learning experience till you know that your learners can actually play Flash once it gets to their machine. For any client, find out what the ACTUAL (not the corporate model) learner platform is, here and in other countries where learners may be located: OS and version, browser and version, soundcard, plug-ins and versions, effective bandwidth budgets etc.
If their system is out of step and can't handle recent generations of Flash, you might as well stop right there. If their systems are more up to date, then installing a recent Flash player may not be a problem -- though your clients' IT and networking people need to be consulted. They have to install and maintain the plug-ins.
And while you are talking to the IT/networking folks, find out about bandwidth policies. I have a client (very large automotive manufacturer) who had an old network infrastructure that might seize up under any even limited use of streaming audio or video, but could just sneak in some limited silent Flash animations. They upgraded the network only this year which opens up more possibilities -- but don't assume that just because a client is a mega-corporation with hi-tech products that it has a hi-tech internal infrastructure. My rule of thumb is the bigger the corporation, the slower it is to upgrade its hardware/software infrastructure (they often skip a generation or two).
Once you know the client infrastructure reality, then you can start deciding on your development tools.