line out, etc...

Yes. The signal will be way hotter than the Elf is expecting though, so be careful with the gain control. You may not be able to turn it down enough and it may sound distorted. The only way is to try though, you can't hurt anything.

 

If the Elf has an fx loop fx return would be better.

You actually CAN hurt something doing it as described in the OP, but it isnt likely, and using caution can prevent it. Keep in mind you are "stacking" pre amps doing it that way so use discretion With the second amp in the chain as far as eq.

 

You will probably want to set the elf at a volume you like with just your bass, then use the line out of the Fender with the gain all the way down, and slowly raise the gain until the volume is similar. The manual says that the preamp controls the line out volume, so the lass gain you use, the lower the signal being sent to the Elf. You’ll just have to balance it all out.

 

I would start with both 'off' and bring them up slowly.