Add Bmesh to another Bmesh I'm using a scrip Subprogram of Animation nodes to merge that will merge a list of objects using Bmesh (Because it holds the UVs) 

But now i'm stuck at merging two Bmesh as the picture below explains.
SO i've managed to do the trick using the answer of CoDEmanX here : enter link description here 
Still very strict to use and have a high ms 

import bpy 

AN= bpy.data.node_groups['NodeTree']
L = AN.nodes["Data Interface"].value

def OB_list_joiner(L,b,n):

    ctx = bpy.context.copy()
    P=[]

    for v in L :
        o=v.copy()
        o.data=v.data.copy()
        P.append(o)

    for v in P:
        bpy.context.scene.objects.link(v)

    ctx['active_object'] = P[0]
    ctx['selected_objects'] = P
    ctx['selected_editable_bases'] = [bpy.context.scene.object_bases[ob.name] for ob in P]
    P[0].name = n
    bpy.ops.object.join(ctx)
    return P[0]

if N not in bpy.data.objects :
    O = OB_list_joiner(L,True,N)
else :
    O = bpy.data.objects[N]