I can't give ALL the compatibilities...I haven't seen some of the brands of equip that are out there. (No idea what pinout/voltage/frequency shift, etc. Multplex uses. And there's more brands.)
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The 2 most common rX/Servo pinouts are the Futaba/JR/Hitech style +,-,S (S= signal) and the Airtronics -,+,S And the newer Airtronics radios have switched to the same pinout as Futaba. Hobico defaults to the Futaba, but will put the old type Airtronics plug/pinout on if you specify it when ordering the servo. (same for most other brands too...)
Plugging an old Airtronics servo into a Futaba RX can fry both the RX and the servo (and any other servos attached...) same for plugging a Futaba servo into an Airtronics. You swap the + and - leads to match and you don't have this problem. Feeding +5 v on the - lead and having the signal lead able to carry the reversed current will fry stuff QUICK.

The Futaba J connector can be trimmed to fit in a JR or "universal" plug. Just trim the alignmnet lug off and a Futaba servo plugs right into a JR RX. You do have to be careful not to plug it in backwards... (especially when plugging back into a Futaba RX)
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There's 2 "shift" modes for the FM radio signals. Futaba/Hitech use - shift and JR uses + shift (I might have the + and - backwards...) As long as you know your radio make and specify that when ordering the RX... should be no problem (except Futaba doesn't make JR compatible RX's and JR doesn't make them for Futaba...) GWS and FMA default to JR compatible if you don't tell them which you want. Hobbico is essentially re-labeled Futaba stuff... I'm not sure which shift mode is used by Airtronics.
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There's a new system out which advertises that its TX AND RX are able to be set for whichever shift mode is desired. (and has synthesized frequency control.. for access to ALL "channels" without changing crystals.) I believe they use the Futaba type servo connection.