NOT! I luv Nikon's dSLRs but their digicams are seemingly made by the marketing division, not the folks who make their dSLRs and actually take pictures. Given their comparable prices, I'd choose a D40 dSLR over the P5100 or any other premium digicam out now.
Frankly, I'd look back a few generations in the megapixel race for a digicamera in the 5-7MP range. More than enough resolution for 8"x11" prints. Generally cleaner ISO performace too than these new 10-12MP models. Maybe hard to find now but you will get better pics and a cheaper camera too! Megapixels are not as important in digiscoping since you can use the 3x-4x OPTICAL zoom of the camera and eyepiece magnification to get insane focal lengths up to 6000mm so you won't be cropping your pics that much.
More important for digiscoping is a good user interface with good manual control of ISO, Exposure, White balance, Shutter Speed (hard to find though), Sharpness, Saturation and Contrast. Quick, easy access to these settings with dedicated buttons is best. You don't want them buried deep in a confusing Menu (ala Nikon) as you will change them often. A realtime histogram display will also be helpfull. Also must have a decent continuous shooting mode too as you will need to fire off multiple exposures to get a sharp pic if the target is moving or you have vibration from wind, etc. A IR remote release option is ideal with 1-2sec delay timer capable of at least 3 conituous exposures a minimum. Finally, an OEM scope designed mounting system helps though their are several third-party solutions that can adapt most cameras to a scope. Worst case is you will have to DIY an adapter, but you will find lots of ideas here in the forums.
FWIW, my digicam of choice is a 4yr old Pentax Optio S5z. If I had a do-over I might choose a Fuji F31 because of its unbeatable ISO performance and great optics. The Canon A5xx series looks nice too.
In the end though, if your goal is to take great pics a dSLR is the way to go.
cheers,
Rick