The rumor is new to me, but could be possible if:
1) Hartwell will be a very difficult man to replace
2) Since more teams want to switch to 3-4, the Ravens might try to take advantage and get higher value players through trading some 3-4 personnel
3) With the loss of Baxter, if the Ravens cannot acquire another big name CB, they might abandon the blitzing ability of the 3-4 for the coverage ability of the 4-3.
Just some thinking off the top of my head. [so if some reasons are more stupid than others.... no one to blame!]
Anyhow, hard for me to see the Ravens abandon the style that's made them the top defense the last few years.