questions regarding bridge mode

[Wolfgang]

Are both bridge and routed mode supported together running both on a gateway?

Are LLDP and CDP packets forwarded in bridge mode, meaning these packets from other devices not the gateways itself ?

I need an answer for regular gateways and for SMB appliances too.

[G_W_Albrecht]

sk101371: Bridge Mode on Gaia OS and SecurePlatform OS

https://sc1.checkpoint.com/documents/R81.20/WebAdminGuides/EN/CP_R81.20_SecurityGateway_Guide/Conten...

SMBs see documantation.

[PhoneBoy]

Assuming you can be 100% sure there will not be a double inspection issue (same packet traverses the gateway twice), yes.
The following applies to LLDP: https://supportcenter.checkpoint.com/supportcenter/portal?eventSubmit_doGoviewsolutiondetails=&solut... 
These limitations should also apply to SMB appliances.