Hey
I'm a musician and lyricist. Much depend on the type of song. Where the rhythm is an important factor (in say dance genres as an example) then I do sometimes write with the drum riff going in the background. Certainly I tap out a simple beat on a regular basis when writing lyrics. I normally write the melody first these days, so when I come to write the lyrics there is already a metre established.
Yet again when it comes to writing the melody I write with at least tapping the beat or a drum pattern going.