Hi Imbracable
VNAV conbined with an engine failure will command an acceleration for flap retraction, giving you close to level flight, but never a descent command via the FD or AP.
There are some traps included in VNAV take-offs:
As far as I know Boeing is not reccomending VNAV T/O´s on the NG since it will not give windshear alerts under certain circumstances. This bug might be fixed on the next update.
Also, if an immediate turn is required being one engine out, the turn radius is usually based on V2-V+20 plus some additional addatives, so accelerating in that phase might bust the obstacle corridor.
If using LNAV as well you should have a procedure to cross check the one engine out profile before T/O since it will give additional stress if the special procedure is not in the box.
My company did LNAV/VNAV T/O´s for a while but went back to 400´LNAV, 800`VNAV since there are too many problems with that procedure. But of course, that is only valid for may company and the software we are using, don`t know about the others.
Hope that helps,
regards
repulo