Looking at buying a 1756 Havoc aluminum boat for duck hunting and fishing.  I will put a Yamaha 50 on it.  Will I want/need a jack plate?  Theses motors have power tilt and trim.

I could put a mud motor on it, but from what I've seen, they are VERY problematic.

You're fine. A jack plate is going to help your rig at all anyway.

??  Is, or is not?

I assume  akethan means it won't help your boat given the hull/transom design. Just keep the water intakes on the lower unit submerged (when trimmed up to extremes)  so it will cool and you should be GTG.

is not, sorry

No they are not the same. Two different effects. You may find benifits with a Jack plate... Shallow water. You can gain a couple inches by moving the engine up and still keep the boats attitude in a running condation. Trimming to far with the engine trim motor places undue stress on both the transom and trim motor. It also causes increased cavation at the lower unit.
The proper way to achieve the most options on your running set up is with a jack plate. Cost benifit is the question..?
If you are not running at speed in areas where you need to watch out hitting bottom then I would say no. If you have areas where you have shallow draft issues then yes you can gain a couple inches. Jack plate was originally designed for optimum engine set up..not to jack your motor up out of the way for rocks, bottom..but is now commonly used for that on many flats boats. You have to be careful when running with a jack plate raised higher than it should be... The boat at speed will be unstable and you could loose steering input.