Should i grail hans?

Understand that Grails are possibly the most valuable resource you have towards improving your servants. Therefore, looking at his stats, a +5 Grail'd Hans only has 11k HP and 7.6k Atk, which is honestly quite pathetic for a Grail'd servant. Unless Hans is your husbando, I would suggest otherwise as there are other, better supports to Lancelot like Waver (He's only story locked so you'll have plenty of chances to get spooked by him). You can also wait 6-8 months for the game-breaking servant that is Merlin to come out, but that's a while away.

Short answer: No.

Long answer: Hans is a support, meaning his value is only from his skills and NP. Having more stats by grailing is obviously appreciated for every servant, but keep in mind that grails are an incredibly rare resource. The opportunity cost of grailing Hans is massive as there are other servants that would be much better to be grailed (SSRs for instance). Hans, even when grailed, won't have impressive stats anyways, so I suggest saving your grails for someone else.

Increase his survivability by having good supports and CEs instead.