If one were to get hired with AMC or REH, what are the chances of going straight to a SPIFR platform like the H135 or H145 with AMC? 

My age (If it matters) and experience are

Age 50, over 7,000 hours rotor single engine turbine time, about 1,000 hours FW RG SE time with some actual IFR but no actual IFR helicopter time (Only simulated). CFI and CFII in both categories. I like the challenge of IFR flying and would prefer to skip getting into a VFR only program. Thanks in advance.

Let'r rip.

I was age 56, hadn't flown in 11 years. 7,000 hours, half helo half fixed. Most of my Helo time in Bell 206 and MD-500, was picked up into an EC-135 SPIFR program. Study your regs, know procedures. 

Even with a strong instrument background the chances of failing at checkride are much greater than with a VFR program. Then if they keep you in a VF our program you have the stigma of sucking out of an IFR program

into it...no matter how much ACTT you have....if you get on with a IFR program..they will put you in that aircraft for at least 6-8 months VFR only to get used to it...THEN look at upgrading you to the SPIFR platform.. but as a new hire or new to the aircraft, you will be VFR for 6-8 months

I went from one SPIFR into another at the IFR rate of pay although I am stuck flying VFR for 6 months as stated above (detrimental if you ask me but irrelevant). The company doesn't want you to fail checkrides so they will usually be pretty good about getting you comfortable in the platform in my experience.

Someone who is hired at a SPIFR program will get trained and be flying the aircraft at your base. That will be an IFR aircraft, but you will be only flying VFR for the first 6 months. That gives a new pilot some time to get used ot the aircaft, the area they are operating in, and how the company likes to do things. They should be giving you some more, IFR specific training, and then at the six month mark, an instrument check ride. 

16 years in HEMS. No more dangerous than any other helicopter job if you make it as safe as you wish it to be. Weather changes, that's the nature of weather. Have a plan to survive that and use the plan ASAP.

Yes, you get called out at oh-dark thirty for a random place. Yes, the pressure is on for an expeditious acceptance and departure. Proper preparation and knowledge are the first steps to safety, but careful, cautious  and conservative evaluation of ad hoc scenes is your ticket to going home with an intact helicopter. I don't know the cliché origin, but: When in doubt there is no doubt- don't do it! 

It was hard for me to adapt to the very, very, very slow and cautious approaches coming from a hundred landings a day job.... But it is the only way: creep in- yeah, you're hanging on the engine. But that's better than hanging on a wire.

careful what you ask for.