I think you bring up a reasonable worry but I'm not 100% sure it's truly a concern. MCPHS is newer/less-established, and that's true. But I would like to think that educators at less established schools aren't necessarily worse than at established schools. There are lots of smart optometrists so anyone who is qualified to get hired at an institution, I'm pretty sure would be competent at teaching primary care optometry. Regarding the pass rates, given that MCPHS is less established than Salus, it could very well be a reflection of the (presumably) weaker student body as opposed to the quality of education. Thus, what I'm saying is that attending MCPHS isn't necessarily going to make you less competitive for the boards as compared to Salus. If anyone here has anecdotal evidence or sound reasoning as to why my reasoning is incorrect here, please do share.
I don't think ODs will necessarily consider a Salus graduate > MCPHS graduate. If both passed boards, I don't really think that would be a (big) factor. Other factors would overwhelm it. Things that come up in an interview like attitude, fit, personality, motivation, etc. would all vastly overwhelm any perceived weakness of MCPHS vs Salus. Again, just my thought. Maybe it would matter in a tie breaker? I don't know.
Provided that MCPHS is accredited and not super spanking-brand-new, I'd probably tell you to go to the place that saves you the most money.