Having run a 'mixed' tank before, I certainly wouldn't recommend it, unless you know exactly what you're doing, or have a very large enclosure.
The RETF will get big enough to eat a house gecko, and probably eat a crestie as well.
You could, however, put a house gecko in with a crestie, they have the same environmental requirements. However, the crestie may get big enough to try to eat the house gecko, in which case you'll have a dead house gecko and a dead crestie.
Be very careful with house geckos, they're mostly wild caught, you don't want a beautiful $300 crestie to get parasites from it. I'd recommend quarantine of the house gecko for at least a 3 month period before introducing them together.