I can confirm that Connect Plus trunking will NOT pass talkgroups through on sites that do NOT have affiliated users present. If I scan from one talkgroup that i am affiliated on, trying to monitor a second talkgroup, unless there is a user on that second talkgroup affiliated to the same site as I am on talkgroup 1, then I will NOT hear traffic on talkgroup 2.
P25 systems have the capability for the controller to be programmed to "always" transmit on all or specified sites. This would typically be done in the case of a countywide alert channel, or FD dispatch talkgroup, where you would have users wanting to scan it and always be able to hear it regardless of what site their selected talkgroup is affiliated on. I believe Connect Plus might have that capability as well, at least according to the MotoTRBO manuals I have perused. Probably not something instituted frequently.
Connect Plus radios have something similar to a "home" site, which is selected in the programming, which tells the radio which site it should try first. It is "site 1" on my Fisher TeamTalk radio, so they probably put more repeaters on that site to handle the default affiliations. If you know which site on the system you monitoring gets the most traffic, would be best to utilize that site for scanning, or if using a MotoTRBO radio, try to affiliate with the most popular site on your talkgroup, to ensure the best chance of scanning your secondary talkgroups for traffic.
Paul