The Blackfin can handle the servos, and it has two UART ports . . . but you may not find coding it to be as easy, and you'd need to wire up a separate power bus to attach servos.
As for the accelerometer, I'm not sure if the Blackfin has ADC. The datasheet isn't so clear . . . you'll have to read up on that.
I'm biased, yes, but my vote says using the Axon (or any other additional multi-UART microcontroller) will make it much easier to make a full robot out of the Blackfin. The advantage with the Axon is that the code is already done for you, easy to hack, and just plug and play. Is this for a one-off robot, or a product?
Try asking Surveyor what they think will be easiest/best for your app, too. I'm definitely no Blackfin expert!