I believe the "No route to host" error could be a red herring. I don't know what particular network stack does this but I've seen cases where connecting to one port returns "No route to host" and another connects successfully. Indeed, that's what I see on this machine right now: connecting via port 80 works and via port 443 doesn't, giving a "no route to host"! This is then not actually an IP routing problem at all.
http://www.pcvr.nl/tcpip/icmp_int.htm#6_6 says that many different ICMP errors are translated into the Unix error "no route to host" (making this error potentially quite misleading in this regard).
I ran a packet sniffer while trying to connect to this host and I saw ICMP code 10 ("Host administratively prohibited"), which my OS nonetheless displayed as "No route to host" even though I don't regard that as a good explanation of the actual ICMP message. (Also, maybe this means that Boulder should somehow try to log this error more specifically, if the sockets interface provides any way to get that detail, although I'm not at all sure that it does.)
Anyway, this suggests a firewall problem to me.