If I understand you correctly, the Greater Vampire is from the Elven campaign, which is actually the fifth one. So, in my opinion, you can do it. Heroes games allow you to progress with any build you like, so to speak – it doesn't have to be the standard one. And in the fifth Heroes game, I don't even upgrade summoning. Firstly, it's not a core magic school, meaning you won't find spells of this school in the native castles – you'll struggle to find them, collect them from the map, and you're unlikely to find higher-level ones. Secondly, the effect of summoning and chaos spells depends on the spellcasting skill, which is also not a core skill for Elves, meaning you shouldn't expect a super-mega phoenix like you would from a Necromancer. No matter how you look at it, upgrading this school is questionable, but it's a matter of taste. I was also upset at first – how can Elves be without summoning? But in the fifth Heroes game, that's the way it is with the magic schools. As for resurrection, it's a pity, but not critical, as I said in the relevant thread. In the last mission, my Frida didn't have it, and it was fine; she still does a good job of taking down enemies. I would gladly give you a save file (I've already managed to get resurrection in this campaign), but I have a different version, which I'm currently fixing so I can complete an earlier mission. Sorry