Your question is way too broad. Firstly what level of Viya developer? A junior, intermediate, senior or expert? What role is on offer? Data analyst, application designer, application builder, application tester, application maintainer, and so on? The standards and requirements will depend on the answers to these questions. Also is the industry you are using Viya in of relevance? In my experience the more senior the role, the more likely an employer will want industry experience.
Please also bear in mind SAS VIya is a very new technology. If a recruiter says you need 10 years SAS Viya experience then he/she is talking rubbish because it hasn't been available for that long. Most SAS sites are only now in the process of migrating from SAS 9 to SAS Viya and it will be years before most use Viya.
In general, someone with good, demonstratable IT and SAS 9 skills should be easily able to transfer those to Viya.