Hi Bethanne--Yes, lupus CAN and OFTEN does cause a false-positive syphillis test. It can also cause a false-positive mono test which happened to me.
I can understand you're wanting to wait to be tested for lupus after you wedding---the dx can take a very long time and if you do have it and get a dx right away--instantly everything changes. I'm sure you are under a lot of stress right now planning your wedding and other things going on in your life so if you aren't experiencing symptoms that are particularly bothersome right now and feel like you can wait--I understand that.
On the other hand, because you had a positive syphillis test, I would think you would want to be able to rule that out right away. If you in fact do have it, that does need to be treated right away--it can cause sterility and can kill you. Not to mention that you can pass it on to your fiance/husband. So, talk to your doctor see what he/she thinks you should do. But under the circumstances, I'd try to get syphills either confirmed or ruled out for sure.