I'm not seeing a ton of simulcast stuff on a quick glance, but someone in the Oregon forum can give you better info. If I didn't have to deal with simulcast systems here, I'd have a 536 instead of the SDS200.
The folks in the Oregon forum will be able to let you know exactly what is in place and possibly any future changes that may influence your need.
Seems to be a fair amount of VHF channels in the area. Some SDS200 owners report lower sensitivity in the VHF band; that's my experience as well. That's another factor to consider. Mine does perform better on VHF in the digital modes.
Portland TG Category: Portland Police Bureau Details
www.radioreference.com
For everyone else listed as mode "D" I'd go with the SDS200 to overcome simulcast distortion you'll likely face monitoring with a 536HP or anything else
Scanner Frequencies and Radio Frequency Reference for Multnomah County, Oregon (OR)
www.radioreference.com
EAFrizzle has good advice to take it to the Oregon forum. It would benefit you if you take some tome and look at Portland and the surrounding area to better understand and to decide what systems that best interest you. I personally use both.