All our servers are currently hosted on Amazon AWS eu-west-1 in Ireland. Below is a list of the IPs Hotjar uses to send egress, outgoing, traffic from which you can whitelist if required on your end.
IPs used for outgoing traffic only.
52.31.130.160
52.19.187.86
52.18.82.24
52.19.110.121
52.30.169.87
52.48.84.127
52.19.220.3
52.51.33.45
52.51.204.189
52.51.178.126
52.30.70.238
52.208.117.195
34.252.143.103
34.248.4.97
34.254.89.100
34.242.169.250
52.212.239.19
52.51.40.151
52.212.240.37
52.48.181.63
34.251.237.25
52.208.238.241
34.252.23.19
34.242.31.66
52.209.246.84
34.240.82.131
34.253.37.83
52.213.52.115
52.215.92.107
54.77.97.4
Note
The IPs listed above do not cover the actual domain https://insights.hotjar.com. This is due to it being configured on an Amazon ELB, Elastic Load Balancer, which means there are multiple non-static IPs assigned to it. If you need to whitelist this as well, the only option would be to whitelist the domains *.hotjar.com
If you need to, you can see a list of all Amazon IPs in this json file, however it is important to know that these IPs change quite regularly.