as long as you avoid trust and relevance issues you'll probably be ok.
are the sites relevant to each other?
are you doing a redirect where every url has an equivalent url with essentially the same content on the new domain?
are you changing the urls other than the hostname?

are the sites relevant to each other?

Yes

are you doing a redirect where every url has an equivalent url with essentially the same content on the new domain?

yes

are you changing the urls other than the hostname?

don't know what you mean by this exactly

are you changing the urls other than the hostname?

don't know what you mean by this exactly

oldexample.com/widgets/red/ gets redirected to newexample.com/widgets/red/ rather than newexample.com/red-widgets/ or even worse redirected to the home page newexample.com/

hmm, yes, the urls would be changing...I've spoken with several people regarding this issue since I've made the post. They say it will have no benefit in terms of boosting a site's ranking after the first site merge...what do you think?