Both players have been training with Glasgow Warriors squad since pre-season, catching the eye of the club's coaching team with their efforts around Scotstoun.
Argentinian international Sordoni became Warrior #341 when selected to make his debut in the opening match of the 2022/23 season, starting the defeat to Benetton before coming off the bench in the victory over Cardiff a week later.
The 24-year-old has been capped four times by his country to date, most recently in The Rugby Championship against New Zealand in November 2020.
Standing at 6'3", the Rosario-born tight-head has represented both the Jaguares and Melbourne Rebels in Super Rugby.
He joins on a two-year contract, subject to visa, adding to the club's long-standing relationship with Argentinian rugby that also includes team-mates Sebastian Cancelliere, Domingo Miotti and Enrique Pieretto.
"I'm really happy to be here," Sordoni told glasgowwarriors.org.
"It feels like one big family, and for me it's an honour to sign permanently.
'The guys have made it really easy to settle in - it's a great group, from the coaches and backroom team to the players, and I've really enjoyed my time so far.
"When you have friends here already like Seba, Domingo and Enrique, it makes everything much easier. Any time I'm missing home, I can always talk to them, go drink mate or have a barbeque!
"I just want to play as much rugby as I can. My dream is just to play as many minutes as I can for this club."
Born in Dumfries, 20-year-old Hiddleston joins on a partnership contract with FOSROC Super6 outfit Stirling Wolves after being invited to train with the Warriors this summer.
Having initially honed his skills at Dumfries Saints and GHA, the hooker - who is also equally comfortable in the back-row - has impressed for the men from Bridgehaugh, catching the eye with his physicality and dynamism with ball in hand.
First called into the Scotland U20 setup ahead of the 2022 U20 Six Nations, Hiddleston has made six appearances in a blue shirt to date, including in the recent Summer Series.
He was also part of the Glasgow side that claimed victory in the Junior 1872 Cup at Scotstoun in November 2021, as well as having boxed competitively outside of his rugby career.
"I'm absolutely over the moon," Hiddleston told glasgowwarriors.org.
"I can't wait to get going. I've learnt so much already since coming into Scotstoun and I_m excited to get stuck in.
"The Wolves have really pushed me on this last year or so, and I'm really grateful to them. The chance to play week in, week out in the Super6 has been massive and the standard has really helped me develop.
"For me, I just want to keep working hard and see how far I can go - I'm going to keep my head down, keep listening to the coaches and try to show what I can do."
On the signings, Franco Smith added: "We're looking forward to continuing to work with both of these exciting front row talents.
"Lucio has impressed us with this work ethic and a grit in both games and in training and has thoroughly earned his long-term contact with us.
"Gregor is someone the club have been watching closely during his time with the Stirling Wolves and we're pleased to be able to offer him the opportunity to grow and develop as part of our squad."