sorry Lynn, thanks for replying but I think you have misunderstood the question: -

a client can use either SQL Server Native Client or .NET Framework Data Provider to connect as long as failover_partner is provided, so as long as the principal and mirror server names are provided in the connection string, as I see it the presence or not of a witness server is irrelevant in allowing the application to redirect following a mirrored database failover - I was just looking for confirmation of that.