There's an excellent documentary on the Lewton DVD boxset which covers Lewton's career at RKO and contains considerable reference to Welles and the fallout from Kane / Ambersons. The documentary places Lewton as a natural successor to Welles, but one who *could* 'play the game' and please moneymen, audience and critics at the same time.
Crucially, Lewton was producing 'B' pictures, not would-be 'prestige' films like Welles, and his budgets would have been a fraction of Kane / Ambersons. 'Cat People' made RKO a lot of money; this is what gave Lewton his leeway, rather than a vindictive rebuttal against Welles on the part of RKO. In spite of everything, had 'Kane' and 'Ambersons' been big moneyspinners, Welles would have been 'forgiven' by RKO (whether he'd have forgiven them or not is another matter...); alas of course, prevailing circumstances and deliberate inteference, among other things, prevented financial success and closed Welles's first Hollywood chapter with some ignominy.
Lewton was a fine craftsman, if not a 'genius'. Welles was also a fine craftsman, but his reputation for 'genius' likely hurt him as much or more than it ever helped him. Welles's attempt to recast himself as a popular entertainer (Jack Benny stand-in, 'Around the World', etc) in the later 40s and early 50s wasn't fooling anyone. Flicks like 'The Stranger', 'Lady from Shanghai' and even 'Touch of Evil' play like highbrow Lewton, though. If Welles had been able to successfully convert his attempted populism to ticket sales, things might have worked out very differently for him. To be able to see Lewton-budget films of the literary classics that Mercury Theatre on the Air turned out... this is perhaps what the Welles's mooted Desilu series in the 50s could have been?
Lewton's unit continued to make populist films (with their lurid titles imposed by the front office) with strong art credentials and psychological depth. He declined the chance to move into 'A' pictures, as he wouldn't have been able to keep his unit together, and made nine excellent little films. Sadly he suffered severe depression and ill-health, and died relatively young.
I'd strongly recommend the Lewton boxset, not just for the (wonderful) films, but for several good commentaries, and the aforementioned documentary, to anyone interested in Welles's early Hollywood career.
Nice article / review here: http://www.nysun.com/article/21282