ALLOW NAT TRAVERSAL IN A CISCO ROUTER FOR A VPN?

The problem is with your Overload NAT by default devices will do NAT first so you must use a route list to permit your overload NAT nets and deny the ones to the VPN otherwise it will always NAT the traffic and thus never match the VPN
ip nat inside source route-map RMAP_1 interface FastEthernet0/0 overload
!
route-map RMAP_1 permit 1
match ip address 106
!
access-list 106 deny ip 10.100.1.0 0.0.0.255 any (VPN net)
access-list 106 permit ip 172.16.1.0 0.0.0.255 any (your net)
ACL order is important
Note Addresses are not yours so just fit the appropriate in

post your run config.

If I understand, you’re saying you need two devices, one inside the 2801 and one outside the 2801 to connect to each other using port 5000.
Your access-list extended inbound_acl
shows a permit for UDP 5000 but not TCP 5000.
Could it be that the connection is TCP?