All creepers are vines, but not all vines are creepers. My understanding is that vines generally refers to any plant that requires support.
- Some vines are active climbers and crawl up their supports, but do so without any assistance. i.e., they climb by twisting around their support or by sticking to the substrate (e.g., those that climb up walls).
- Other climbing vines send out tendrils/twines to cling on to supports (e.g., climbing beans).
- Some vines don't grow vigorously, but just require support to stay erect and bear fruit.
- creepers are those that grow horizontally and spread out on the ground, creating support for itself as it spreads by rooting its twines as necessary.
Coming to your question, I am not certain they should necessarily be synonyms, but they could be. I'd suggest for now that we use both vines and creepers if the question is about the latter, so as to make the distinction clear (just like vegetables and root-vegetables).