This may be a silly question, but can I use both Digital and Analog servos with the Software Servo library?
What do you mean by "digital servo"?
Do you mean a servo that takes standard PPM RC control signals, and using an internal microcontroller, updates the position at a quicker rate? Example:http://www.hobbypartz.com/servos1.html
...or do you mean a servo that uses a digital bus (and is programmable, has various feedback via bus, etc)? Example:http://www.robotis.com/xe/dynamixel_en
If the former, it shouldn't be an issue; if the latter - then no; not without some kind of method of conversion (which would almost defeat the purpose of these specialized servos).