VLAN ID means tagging?
Jorge doesn't help me much the APs (on VLAN1-Default) work fine and are connected to the M4100-D12G as untagged. The APs, in addition to the management LAN (as mentioned above VLAN1) have other SSIDs, each configured with its own VLAN ID (which in my opinion, and the purpose of this question, means tagging all the devices contained); these other SSIDs are also linked to the M4100-D12G as tagged but I can't "communicate" with them (and vice versa)
It depends. There AP needs its network settings (IP, Mask, GW, OV2500 IP address if present, DNS servers, etc.) That information is obtained using the untagged/native vlan. Then, you have to configure the SSID or UNP/ARP (User Network Profile/Access Role Profile), and map then entire SSID to a VLAN, that can be untagged/native or tagged. Or you can use the ARP schema to map a set of N ARPs to different M VLANs (whatever N and M, with N=M as the case where each ARP is linked with a different VLAN) VLAN-ID = 0 means linked with untagged/native VLAN in that port. Any other number means the traffic will be tagged with such 802.1Q VLAN-ID.
Untagged/native VLAN can be use for both management and service traffic.
Let me know if that helps, Jorge