SIC is allowed to be logged so long as there is the completion of a 135.293 checkride. Some EAS cities put in their contracts with 135 operators serving them that the aircraft will be flown with two pilots. There are a few places out there like Seaport and uh... Pac... Pac... *takes a shot of whiskey* Pacific Wings that'll hire with 400-500 hours TT as SIC. One thing about the single pilot plane SIC time, as I myself have a logbook full of it, that time is worthless without proof of the 135.293 paperwork and checkride. There have been instances in the past of pilots showing up to interviews with their logbooks and no proof the time logged was legal and being sent home.
Cape Air has bridge programs with universities to get hired as an SIC/Intern but I know from conversations (not fact just conversation) with my friends flying out of STL that the mins to to get hired now are solid at 1000TT for everyone else.