I have no real experience with internal hubs or their maintenance but know loads about dirt, grime and water as a year round, high mileage, commuter in Vancouver, Canada. Dirt and grime are expected and will be on your chain, chainring and rear cog regardless of whether you have internal or external gearing. This is not going to change unless your drive train is enclosed. The biggest issue with dirt and grime is making sure your wife doesn't notice you tracked it into the house.
The difference with the internal gearing is that you will have a single chainring and cog subjected to this goop. You will also have the additional advantage of having a constant chainline, presumably the chainline will be straight as opposed to running at varying angles based on the chosen gear and it will obviously not be subjected to the relatively tight bends associated with running on an 11 tooth cog. This in itself should make your chain last longer, which in turn should reduce wear on the chainring and cog.
Water is a different beast though, you will be hard pressed to find a front or rear hub that will keep water out if your commute is prone to turning into a series of lakes connected by small islands of pavement. Once the water gets in the grease become contaminated and bad things start happening to bearings, etc.
Rather than buying hubs with a grease fittings or going on a quest for the ultimate water seal I have become proficient at overhauling my hubs. I use all sorts of grease with glorious claims of being water proof but it doesn't seem to matter much. I am not sure whether the Nexus hubs are good at keeping water out but I would guess that when it does get in you will need to rebuild the hub, this is likely to be a pretty involved operation. Someone else may be able to comment on how frequently that may need to be done and how hard it is. (take their advice with a grain of salt if they tell you they have been commuting year round in Phoenix for the past umpteen years) If you are a fairweather commuter this will be largely irrelevant.
As for the suitability of the bike for your commute. What you want to determine is what range of gearing the drive train will give you and whether or not this will suit your needs. You can figure this out by using the specs provided on the Jamis site (chaing ring 42, sprocket 20) with the calculator on this page. http://www.sheldonbrown.com/nexus8/
. If you find that you have trouble with the hills you can always go to a smaller chainring in the front but that will of course mean your feet will be creating a blurred circle like the road runner when you are trying to pedal on a downhill.
I think the bike looks like a reasonable shorter distance commuter. The riding position may be more upright than you would want to over a longer haul. At under 29 pounds it is a pretty lightweight ride compared with some of the other bikes in this genre. I would be be inclined to replace the suspension seat post but you may be partial to bobbing and weaving. REI sells a couple house brand bikes with Nexus hubs that you may want to compare.