Absolutely. When you first signup as a reseller you get a YOURCMS.yikesite.com domain name. However, you also get an unbranded domain name like YOURCMS.customerhost.com which you can use temporarily until you point your domain name.
If you don't have a wildcard domain name pointed, your customers will get a URL like CUSTOMER.clientwebsite.net. When you point your domain name, they will signup to CUSTOMER.<your-domain-name>.
Most domain name registrars will allow you to point a wildcard domain name at our server. What you need to do is make a CNAME for your * wildcard to app.yikesite.com or an A record to 188.8.131.52. Some registrars will charge you additional to do this but registrars like GoDaddy will do this for free.