They will compete for the moisture but if you mulch there shouldn't be a problem except if they grow out of bounds, where you don't want them to grow.

Here is a link that might be useful: Propagating Perennials

Thanks bull,
I was weeding the area yesterday and noticed a few things.
1. the soil there is much better than in other areas of the yard, it was moist (we had 30 minutes of rain saturday and no rain for a week prior.) and I found earthworms and other critters.
2. I noticed there were fewer weeds than last year, and less bermudagrass creeping in. yes I have two invasives competing, vinca next to a bermudagrass lawn. As the vinca thickens and gets taller, the bermuda that creeps in can't get enough sun. Pretty cool.
3. The vinca is creeping into other areas but all very slowly, it's still nothing like what I would call an invasive (like bermudagrass).

Thanks for the help.