There's no clear answer to that, that's up to its viewers to decide. There's a collaborative project, based on Shin Godzilla, Shin Ultraman and Shin Kamen Rider. While the mentioned project doesn't indicate on-screen crossovers because of the fact different companies own these characters, it still suggest connection between the mentioned films. The title of Shin Godzilla also appears in Shin Ultraman in the way the title of Ultra Q appears in Ultraman (1967), suggesting that Shin Ultraman is a follow-up to Shin Godzilla. Shin Godzilla's design was also modified for Gomess in Shin Ultraman. To sum it up, the rights don't allow true on-screen crossovers but there's in fact some connections between the movies.
