Ok, I circled up with another mod on this, @suetli19, and this approach is a bad idea. 
Each base in your paired-end reads gets its own quality score from the sequencer. When a software tool joins two paired ends into one read, it needs to make a choice about what quality score to assign to the positions where the two reads overlap, so quality data gets lost.
As discussed in this topic, assigning new quality scores like this can mess with DADA 2's error model (which uses quality scores for denoising). Your results won't reflect the actual quality scores assigned to the reads during sequencing, and may be less meaningful because of that.
Deblur doesn't care about quality scores. Feel free to experiment with pre-joining and denoising with deblur, but I'd recommend you avoid running pre-joined reads through DADA2.