The engine is allways in development (untill a new one replaces it, anyway), so this is basically how it's gone:
Unreal: UE1
UT: UE1.5
UT2003: UE2
UT2004: UE2.5
UT3: UE3
UE4 isen't out yet as you noted, and is apparently beeing designed for the new Console generation (Xbox720 and PS4), and PC support will be added later (yeah.. i don't think that sounds too promising for us PC-gamers either), and since UT3 bombed, hard, they might not try to launch the UE4 engine with an UT title, more likely, it will be a Console title along the lines of Gears of War, as Epic is mainly a Console developer now.
Red Orchestra was first released for UT2003 as a mod, then ported to UT2004 when that came out, and then went retail from there, so it stacks up like this:
ROmod1: UE2
ROmod2: UE2.5
RO-Ost (retail): UE2.5 (modified)
RO-HoS (retail): UE3 (modified)
So yeah, HoS will use the same engine as UT3, but a newer and better version of it, and the engine will include som new stuff added by TWI themselves (Developers will often modify engines a bit to better support what their games need, with RO:Ost for instance, TWI added Bloom and Motion-blur support to the UE2.5 engine, to support the "suppression" effects they needed, and upgrade it's looks a bit, we don't know what they have added to the UE3 engine yet, but they have confimed that they have modified it in some way).
Maybe it was the other way around, it's been a while since that aired, but i do recall hearing it and thinking "Wait.. did he just confuse DX10 and DX11!?", but i was listening to the edited cast, not live, so i coulen't ask.