You DON'T need interface aliases in order to have multiple IP addresses for the same server. You should use interface aliases mostly if you are dealing with separate subnets and need to route between the addresses, which doesn't seem to be the case.
With Linux (since 2.2 or 2.4, I don't remember) a single interface may have many addresses. This is the preferred way of setting it up. There are issues with the multiple aliases setup, for example, it is not clear how a broadcast message should be handled if multiple aliases are on the same subnet.
I don't know how you set this in Gentoo configuration, but using the standard
ip interface, it is simple:
ip addr add ip1/prefix brd + dev eth0
ip addr add ip2/prefix dev eth0
ip addr add ip3/prefix dev eth0
ip addr add ip4/prefix dev eth0
ip addr add ip5/prefix dev eth0
ip addr add ip6/prefix dev eth0
Note 1: Broadcasts will be received only by the first address. If your addresses are on different subnets, you may want to set broadcasts on the other IPs also.
ifconfig won't probably show the additional addresses, it is obsolete anyways. Use
ip addr show to check which addresses are assigned to each network interface.
Anyways, answering your question: no. Each alias is viewed as a different interface for the system. So eth0 would be one interface, with one address, eth0:0 would be another interface with another address and so on.