"Is this connection (Hermosa park road/ CR 578) paved and passable?"
No and sometimes (but not now) are the short answers.
I think this describes Bolam Pass Road. Because of the large snowpack in the San Juans this year, back road passes will be open later than usual.
This site
http://bushducks.com/tripreps/passopen.htm#bolam (and there are many others) gives a little idea.
bobbin posted the quickest and easiest (thru Mancos) and, while this way is nice, Hooch posted the most scenic and diverse, up and over 2 high passes (thru Silverton) plus over Dallas divide, paved all the way.
Happy trails-