I'd bet that content created in Flash Pro 8 and Fireworks 8 would be compatible with Dreamweaver CS5.5, though I'm not absolutely certain of it (and I'm not quite sure what you mean by "upload"). However, I'm definitely wondering why you're interested in upgrading Dreamweaver but not the other two applications.
If you're serious about taking the leap, you can download Dreamweaver CS5.5 as a 30-day trial before purchasing, to see how it works in conjunction with those applications.
Be aware that CS6 is just around the corner. You may want to wait just a bit and try that instead. On the other hand, if you were to purchase Dreamweaver CS5.5 now, you'd probably qualify for an automatic upgrade to the CS6 version when it's released.
Also, Adobe's now pushing its "Creative Cloud", which is a monthly membership option that includes all the Creative Suite applications plus some new web-oriented applications that might be of interest to you, such as Adobe Muse.
Thanks for the assistance and the info. Much appreciated.