We don't know who imprisoned Veidt, there is some indication it could have been Lady Trieu, and not Dr. Manhattan.
As for timeline, everything in Watchmen GN happened, then it appears that sometime in the 2000s (?) Dr. Manhattan courts Sister Night while she is a cop in Vietnam. We don't know why, but I would speculate he had to do it for some payoff later... but who the fuck knows.
I'm interested to see where Silk Specter falls, will this make her hate Sister Night? Will Lady Trieu end up being her half-sister? (there are hints that her mother was the woman the Comedian impregnated in Vietnam in the GN)