Reverb effects - guitar effects pedals and line levels

I've an Etherwave Standard, playing 'classical'/notes. I'd like to add a bit of presence/atmosphere to my sound, so have considered reverb (I like the look of a Tonebug Reverb).

However, I'm aware the Etherwave Standard has a line out, rather than guitar-level output - is this a problem with effects pedals designed for guitars?

Yes and no ...

You might need to use a volume pedal (quickest off-the-shelf solution) or build an attenuator between your theremin and the effects pedal to keep from driving it to clipping.