Any printer will clog without use.
Pigment inks are more likely to clog however.
At the same time the toughness of pigment inks is wonderful, and i would not go back to dye inks ever again.
I have an epson 3800 a2 pigment ink printer, its very good, before this I had canon a3+ dye ink printer. The main reason I swapped was because the dye inks are too fragile, unless you frame the prints behind glass they would get damaged half the time, you certainly could not give clients raw prints from a dye printer and expect them not to 'break' them.
As far as clogging goes, yes it will clog up after 3 months with no use half the heads will be blocked (i went on holiday) but the printers cleaning mechanism will clean it no problem in a few passes. After 3 weeks, a couple heads will be blocked and it will clean off easily with the printers cleaning mechanism in one go.
Its very easy to see if the printers heads are good, you just run a head check and it prints a line for each nossle, so if there is a break in the line it needs a clean. I run a head check before any photo prints go through.
also a2 printers are far cheaper to run than a3 printers... Half the cost in ink. They pay for themselves after one refill.
The only reason why one printer might not clog up is if its running a cleaning operation every time you turn it on or the printer driver runs one every so often based on the date and time it was last turned on. This just wastes ink if the clean isn't really needed, so I do it manually. (all consumer grade printers will do this)
As for my opinion specifically on the pro 9000 is that its only an a3 printer, do the math on the cost of ink vs the a2, and Dye inks suck.