Define "other energy weapons". If you mean a lascannon, multimelta, or heavy flamer; well, a heavy flamer attatchment is capable on terminator armour, but its frowned upon because of chaos champions using them and the such. The lascannon and multi-melta is because (like troy said) tactical dreadnought armour has no room to put an energy source in to power them, since they don't have back packs. Terminator armour, following the codex astartes, utilizes heavy immpact/ballistic weaponry.
Now back to my awesome idea for the "ego marine" There is no fluff saying there isn't a space marine character with tons of charisma and mojo about him. Its not like people will have a hard time killing him, a large blast does the job pretty well.