Most likely not. Knitting with 2 strands together makes your stitches a little more bulky. SO you are not going to get the same gauge you would if you were knitting with two strands. However, I think this is generally easy to fix by doing a gauge swatch and following your gauge for your measurements. You aren't going to be able to follow the pattern exactly because of the change. The increases and decreases won't make too huge of a difference.
I think its best to have a good understanding of what you are doing in the pattern so that you can alter as needed. If you aren't all that great with adapting a pattern to suit your own needs it might not be best to deviate from the two strands.