Soap UI 5.x versions are currently unusable from the last 2.x versions of selenium up to version 3.X. This is due to dependency mismatches in the http client which prevent inter-operability in the same JVM. Soap UI is a viable solutions for web testing with Selenium, we used it for many years in the past. Currently it is unusable.
This is a very nice way to do web testing when it works, and many folks have asked about this.